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The Success Rates of Arizona Fall League All Stars

Players are sent to the Arizona Fall League for all sorts of reasons. The MLB-owned prospect-laden fall league serves as a domestic winter league, and so teams use it as they wish. But once you are selected as an all-star, an AFL Rising Star, you’ve got a unique stamp of approval, something akin to being an all-star in a league of all-stars. And now that the Rising Stars game has been around since 2006, we have some data to see exactly what that selection means for a prospect.

Some teams send players to Arizona because they were injured during the year and need to build up arm strength, innings pitched, or plate appearances. Some teams send players to try out a new position. Some teams send fast-track prospects from the low minors so that they preview what play in the high minors will look like. Some teams send polished picks straight from the college ranks so that they can skip a level on their way to the bigs. Some teams send prospects they might like to trade so that they might look better to future trade partners after some time in the offensive-friendly league. Most teams send players that face the Rule 5 draft if they aren’t moved to the forty-man roster.

That makes for an eclectic mix. Kris Bryant, with all of 143 low-minors plate appearances off of being selected number two in the draft this season, facing Drew Hutchison with his major-league experience and coming off elbow surgery. Kyle Parker, five years older than his shortstop, Addison Russell. Unfamiliar hordes of pitchers, and then Alex Meyer, sticking out with his 99 mph no-seamer.

It’s a great experience. But with the thin desert air, the elevations, and the lack of quality pitching, it’s hard to account correctly for the numbers that players produce. Kris Bryant has hit .365/.448/.743 this season at the AFL so far… and doesn’t lead the league in OPS. Alex Meyer leads the league in strikeouts with 25, but wasn’t allowed to throw five innings until the last week in October due to strict pitch counts from the parent organization. He was throwing 99s and 100s on the gun in short stints.

All of that aside, it’s fair to say that selection to the Rising Stars game is an honor. When I talked to Mookie Betts, Stephen Piscotty and Addison Russell at the game, they all mentioned the fact that they enjoyed being surrounded by and competing against such great talent. This year’s squads included Byron Buxton, Jorge Soler, Alen Hanson, Austin Hedges, and Corey Seager next to the aforementioned players. All of them will figure in highly in the prospect lists as they come out.

So how do they stack up in terms of major league success?

Using the Rising Stars rosters between 2006 (the first iteration of the game) and 2011 (in order to give prospects some time to hit the majors), I set out to answer that question. “Success” was defined as 1.5 WAR per 600 plate appearances or 150 innings pitched since the MLB samples for some of these players were small. Given all the disparate reasons a player can be sent to the AFL, the statistical outcomes from the data set ranged from expected to surprising.

Overall, the position player Rising Stars succeeded in the big leagues 31% of the time. That’s about on par with the overall success rates for prospects just outside Baseball America’s top 30 according to research by Scott McKinney at Royals Review. Maybe not on par with a top-ten prospect, but they can’t all be top ten prospects. And, since many of these prospects are not yet on the Baseball America top 100 list, that’s a happy finding for the Rising Stars. (The average ranked prospect in Arizona is also usually around 50, so they’re overperformers as a group.)

Considering that some AFLers were older players fighting for their roster slot, and some were hotshot younger guys tearing through a minor league system, it seemed to make sense to break up the Rising Stars into separate groups in order to test their success rates further:

Success 31.4%
Success, non-C 30.5%
Pre-AA Success 25.7%
Pre-AAA Success 25.4%
<21 Success 36.8%
<21 Success, non-C 38.9%
<23 Success 33.7%

The fact that younger players do better is no surprise. Examining a player’s age with respect to the average age of his league is a long-established feature of prospect analysis. The older, more physically developed players are closer to their peak and own a natural advantage over younger players. Plus there’s the fact that these organizations are so enamored with a young player that they are already preparing them for their future jumps to higher levels — that bodes well for the young man’s future.

The reason catchers are broken out is less straight forward. It’s not necessarily that catchers do worse than other position players — they do have worse ‘superior’ rates than any position save second — but it’s more about how the AFL is structured. Teams choose their positions via a ‘draft’ during the season. One team picks a shortstop slot, the next an outfield slot, and so on. Most often, they have a player in mind for that slot. Given the depth of catching prospects around the league, should the player that was earmarked for the AFL go down, it’s no given that the team with a catcher slot would have a great option behind him. That might be how Boston’s Dusty Brown — a 25-year-old in Triple-A — got included in this sample.

In any case, once you break catchers out and focus on young position players in the AFL Rising Stars game, you actually land right between the success rates for top-20 (50+%) and top-30 hitting prospects (30%) by Baseball America. The youngest position player all-stars this year include Addison Russell, Albert Almora, Alen Hanson, Corey Seager, Jorge Bonifacio and Byron Buxton.

The position players were far ahead of their pitching brethren, as was to be expected. Pitchers in the sample only succeeded 16% of the time. There’s only so far you can dream upon a group of guys fighting for 40-man roster slots and a chance at a major league bullpen mixed in with guys returning from injuries. The pitching was slightly better this year, as the league slugging slipped below .400 for the first time in a while and big names like Kyle Crick and Alex Meyer did well, but it’s not a group to depend upon.

Finally, there’s the idea that many of the prospects in Arizona are there for showcasing. Where better to put your positional prospect that you think has a few warts than the desert, against iffy arms? And in a league that’s heavily scouted, no less. Over the course of the sample, 36% of the positional prospects that appeared in the Rising Stars list were eventually traded. To put that in context, 41% of the position players that appeared on Baseball America’s top 100 list over that same time frame were traded. And it doesn’t get any better if you focus on the top 30 position players on the BA list — 47% of them were traded.

It doesn’t look like the Rising Stars of the Arizona Fall League are more likely to be traded than your average top prospect. And it doesn’t look like the AFL’s pitchers are a great bet. On the other hand, if you’re looking at a young, non-catcher position player prospect that hasn’t appeared in a Baseball America top 100 list yet — like, say a young Mookie Betts — and he appears in the AFL Rising Stars game, well then you’re looking at someone that has approximately the same chance of major league success as a top-25 hitting prospect. And that’s worth a trip to the desert to see.