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Aidan Miller is a fantasy baseball prospect sleeper and potential waiver wire stash. Matt's suite of fundamentals-rooted tools evaluate his dynasty outlook.
Phillies prospect Aidan Miller first caught my ear while watching a batting cage session quartet that included now Tigers prospects Kevin McGonigle and Max Clark during the August 2022 USA Baseball 18 Under (18U) National Team Training/Cut Camp at the Twins complex site in Fort Myers, Florida.
Audibly and easily, Miller packed the loudest bat of the foursome. His swing had not produced much impact in camp intra-squad games but soon erupted in exhibitions played after the final roster selection. The outburst extended into World Baseball and Softball Confederation 18U Baseball World Cup tournament play convened at the Pirates and Orioles Gulf Coast facilities.
This article offers a dynasty fantasy baseball prospect outlook for Miller, based on my scouting and fundamentals-rooted evaluation tools.
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August Through September 2022 Live Looks
Miller had a muted four-game camp stint, going one for nine with a single and a strikeout. Beyond the referenced cage session, on-field batting practices near the end of the camp hinted that something loud may be brewing. He made the team perhaps on potential as much as performance.
A few exhibition friendlies came next as international teams sought to get their baseball legs under them before the Florida Gulf Coast tourney got underway. Miller would emerge early that week as the lineup's primary righthanded power source via a mix of doubles, triples, and homers that extended into the first week of World Cup round-robin pool play.
In that first week of tournament action at the Pirates Bradenton and Orioles Sarasota spring stadiums, Miller drove triples and homers from just right of straightaway center to straightaway left.
Miller line-singled to center on this inbound fastball from Korea fireballer Seohyeon Kim, who topped 100 mph a handful of times during this tournament
Opponents would soon pivot to his seeing mostly righthanded breakers moving away from him, and that tactical strategy was successful in sapping his power as he produced mostly a mix of walks, singles, popups, and strikeouts from then onward. The ability of the powerful righthanded batter to drive that variety of breakers to the right field seemed not to be in the toolkit.
Despite maybe only stealing one base in one try from camp through the tourney finale, Miller seemed a sneaky good offensive runner between the triples and other running-relevant events.
Miller began the August-September stint as a third baseman but ended it as a right fielder else left fielder as players were shuffled defensively to maximize the quality of the batting lineup. He looked solid at third.
He looked even better at the outfield corners where his plus arm repeatedly showed up, most prominently in turning a World Cup sacrifice fly attempt to right into a double play that ended at the plate.
Prospect Analysis: Aidan Miller
Evolution of Pro Plate Profile
Miller was considered a candidate to be selected inside the first ten picks of the 2023 MLB Draft. But on Day One he slid all the way down to the Phillies at pick 27, where he agreed to a slighter overslot bonus.
His 2023 pro debut began with 36 plate appearances with the Rookie Florida Complex Affiliate team before ending with 69 more via the also-Clearwater-based Low-A Florida State League club.
Miller flashed fairly good hit fundamentals that skewed higher in LD + Pull GB Avoid but low on IFFB Avoid. He produced OFFB but not Pull OFFB with Rookie club. He likely acclimated to pro-caliber fastball velocity in Low-A and found the missing Pull OFFB to make more ISO than before.
The 2023 hit-over-power (LD >> OFFB or Pull OFFB; AVG >> ISO) skew was not so in line with how I had projected him based on the prior summer looks. At both stops, plate appearance Overall outcomes were much better against the opposite-handed pitchers that the right batter saw less than they were against the same-handed pitchers he saw more often.
Miller returned to the Low-A affiliate to open 2024 and turned in another 182 PA before joining the High-A club in New Jersey for 257 more. BB+HBP and Batted Ball Profile in 2024 Low-A each represented higher marks than were earned at either 2023 stop.
He pulled OFFB quite often then and enough to generate 90 ISO on Batted Balls. AVG on Batted Balls was also high at 89, and despite LD and Pull GB Avoid each falling versus 2023 and IFFB staying down as before.
The High-A stint featured solid to good BB+HBP and K Avoid outcomes, but Batted Ball Profile rated less than double minus as it was very short on all of LD, Pull OFFB, and IFFB Avoid. Per circa half plus AVG and ISO outcomes with that club, Miller had become a hitter who leaned more on exit velocity than traditional launch and spray fundamentals to generate hits and extra bases.
Miller would end his 2024 campaign with the Double-A team, which played more weeks into September than the High-A squad did. Those final 22 plate trips begat LD and Pull OFFB but neither AVG nor ISO. At both the Low-A and High-A affiliates and as was true during 2023, Miller turned in relatively poorer plate appearances against same-handed pitchers.
In the 2025 MLB spring games, Miller logged 14 plate trips that featured many BB+HBP and an average K frequency. Batted Ball Profile was again thin in LD, Pull OFFB, and IFFB Avoid and produced only a limited amount of AVG and ISO.
Easiest flaw to spot in the plate profile evolution shows up in IFFB Avoid column. Miller has popped up on the infield too much, ultimately limiting both AVG and ISO production on batted balls.
Miller also suffered key 2024 losses in LD and Pull GB Avoid versus 2023, further limiting AVG production. The same-handed pitchers deficits of 2024 were owed mostly to down non-batted-ball BB+HBP and K Avoid outcomes, which suggests that he had trouble reading righthanded breaking balls.
Evolution of Pro Offensive Running
The 6-foot-1, 205-pounder has been fairly aggressive at base stealing. Four steals in five tries during the briefer 2023 debut grew to 23 steals in 28 tries in 2024 play.
On an all-around basis, Miller has rated as a circa half plus offensive runner in each pro season to date. These results dovetail nicely with how I evaluated his offensive running during the 2022 stint on the USA 18U circuit of events.
Dynasty Fantasy Baseball Focus
Miller was reassigned to the Double-A squad to begin 2025, which already skews dubious for reasons discussed earlier. With the caveat that the Phillies also entered what they saw on spring backfield minor league games into such decisions, there was just too much off about the plate profile with the 2024 High-A affiliate.
Phillies may have been blind to that a 2nd percentile batted ball profile very short on LD, Pull OFFB, and IFFB Avoid was lurking beneath circa half plus AVG and ISO outcomes at the level. Meanwhile, that same High-A stint featured the widest gap by which same-handed pitchers outcomes lagged opposite-handed pitchers ones.
For these reasons, expect Miller's cold start to 2025 to extend a few more months. Dynasty fantasy owners should hold Miller owing to likelier overassignment at present.
They should also suspect that the plate profile areas in which he grades out short during earlier 2025 Double-A play stand to be the same ones that give him trouble in an MLB debut. Non-owners might consider a well-timed "acquire while stock is down" move.
In the case of a recent prep draft signee who needs a fair amount of pro development, focus more on the present player than projecting a future MLB player. Plate profile now features average to half plus BB+HBP, half plus K Avoid, and a half minus Batted Ball Profile that skews shorter on key elements LD, Pull OFFB, and IFFB Avoid.
Actual AVG and ISO outcomes somewhat expected outcomes and such would be owed to the player usually hitting the ball reasonably hard. The righty batter likely did not read same-handed spin so well per 2024 non-batted-ball struggles with righthanded pitchers.
Miller is a good offensive runner on an all-around basis and should steal twenty to thirty bases in fuller minor league seasons.
As a pro, Miller has played only one position and it has yet to be mentioned in this article. Statistics paint him as reasonably competent as a pro shortstop but he figures to be increasingly stretched thin there ahead.
His real-world and fantasy value increases by playing both third base and right field better than he now plays shortstop, where he could perhaps spot start when necessary in earlier years of his MLB career.
The potential defensive positional spectrum, offensive running forecast, and a louder work-in-progress bat conjures up memories of a younger Kris Bryant though Miller has yet to flash that level of power as a professional.
Brief Explanation of the FaBIO Model
My Fielding- and Ballpark-Independent Outcomes (FaBIO) evaluation model sorts every plate appearance into one of 12 outcome bins (BB+HBP, K, IFFB, Pull-Third OFFB, Center-Third OFFB, Oppo-Third OFFB, Pull-Third LD, Center-Third LD, Oppo-Third LD, Pull-Third GB, Center-Third GB, Oppo-Third GB) and charges the pitcher and batter with their league's mean runs value for said particular event that season.
Dividing a batter's total number of expected runs by plate appearance (PA) yields expected runs per PA that can be percentile ranked relative to the league mean and standard deviation for that parameter amongst league batter qualifiers to arrive at their Overall Rating.
Its three subcomponents of BB+HBP Rating (based on BB+HBP per PA), Strikeout Avoid Rating (K Avoid, based on K per PA), and Batted Ball Profile Rating (expected runs per batted ball) are also reported to identify the path the batter traveled to reach their Overall Rating.
Overall Rating and Batted Ball Profile Rating of batters should be considered power- and speed-neutralized metrics since the real-world runs value of a single batter's typical OFFB or LD varies with their strength, and the expected runs value of their typical GB varies with their speed.
To better understand the Path to Batted Ball Profile, we will also examine percentile ratings for select batted ball event types (on a per-batted ball basis). To check how well expected batted ball outcomes match real-world ones, we will compute percentile ratings for hits (AVG) and isolated power (ISO, or simply extra bases) on batted balls (recognizing full well that these two parameters are neither fielding- nor ballpark-independent outcomes).
What most explains a batter's ability to generate hits (AVG) on batted balls is any LD, IFFB avoidance, Pull-Third OFFB, and Pull-Third GB avoidance. What most explains their ability to generate extra bases (ISO) on batted balls is any OFFB, Pull-Third OFFB, Pull-Third LD, and IFFB avoidance.
A percentile rating of 97 amounts to plus-plus (two standard deviations above the mean), 84 is plus (one standard deviation above the mean), 69 is half plus, 50 is average, 31 is half minus, 16 is minus, and three is minus-minus.
A new addition to this suite of evaluation models is the Offensive Running Rating. This tool quantifies how each relevant inning's run expectancy was impacted by the player's action or inaction as either a batter or baserunner on very specific types of plays that are more likely to involve one or both of their speed or offensive running techniques, plus acumen.
The evaluated batter and baserunner events are summarized in the graphic.
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