Looking at the Mariners’ minor league seasons through composite stats

We love numbers here. Some of our best friends are numbers. They are tools to counterbalance what our eyes and instincts tell us, at times challenging or confirming preconceptions. Evaluating baseball players with limited access to interviews, practices, and clubhouses means we rely on data more than most. Doing that in the minor leagues, where Statcast info is not public knowledge aside from a trickle revealed on broadcasts by caring broadcasters, is a bear. Even finding splits data is a fairly recent development.

But one of the trickiest things to do is gauge what data matters, and how much credence to lend it. We need sample sizes, context, ease of use, and most of all, more information, always. One of the best tools for measuring hitters at the big league level is Weighted Runs Created Plus (wRC+), because it builds a great deal of context into itself. The stat is based on a scale where 100 is league-average and every number above or below is that percent better than MLB is averaging that year (ease of use!). The stat weights different types of offense to what we can best estimate leads to runs (e.g. doubles do a good degree more towards run production, though not exactly twice as much as a single), and considers the park at which the events occurred (context!). We have to apply the sample size ourselves, gauging how the player came by their production (is their BABIP sky-high? Is their OBP driven by HBPs?). But for minor leaguers it’s not typically that simple.

We have some context for minor league hitters. Triple slash lines of BA/OBP/SLG, K% and BB%, whiff rates, and isolated power can all be found online, and of course in-person scouting and reports from professional scouts help us put together the puzzle. We even benefit from research on which stats correlate best from the minors to the big leagues! We can even see how wRC+ correlates from the minors to the bigs (the answer is it’s okay at higher levels, less so at lower levels). In our writing we try to add more context, like that both Modesto and Arkansas play in the most pitcher-friendly parks in their respective leagues, hurting hitters but helping their pitching numbers. It helps to have numbers that meet you in the middle on context, and that is part of the appeal of Baseball Prospectus’ Deserved Runs Created Plus (DRC+).

The stat is measured on the same scale as wRC+, with DRC+ attempting to measure the quality of contact made and bake some of the expected results of contact into the calculation. The calculation itself is proprietary, but it rewards hitters partially for the results (what happened) and partially, in theory, for the process (what was likeliest to happen based on how/where the ball was hit). It also regresses the numbers towards the mean expectations for their process, attempting to provide more appropriate estimations in smaller sample sizes.

This is where I will recommend you go subscribe to BP yourself.

Another notable difference between the two measurements is that while wRC+ weights minor league data based on league-wide average park factors, DRC+ does so on a park-by-park basis as both metrics do at the MLB level. The risk there is that minor league park factors are more prone to fluctuation from year to year, whereas league-wide ones shift less. On the other hand, multi-year park factors offer a bit more confidence, and players whose home fields are in extreme parks for their leagues may be overly favored or dinged by wRC+.

I pulled the data from both metrics, as well as good ‘ol OPS, for every Mariners minor leaguer with at least 250 PAs at one level this year (DRC+ doesn’t have combined multi-level data) so we can get a sense of how most of the M’s notable youngsters stack up. (Jarred Kelenic fell short at 218/190/92 PA at A/A+/AA respectively but his wRC+ and DRC+ numbers are nearly identical at each stage: 181/129/133 wRC+, 181/138/134 DRC+):

I’m not particularly inclined to draw strong conclusions from this, but there are a few things that stand out in this table.

• Every single hitter in AA-Arkansas is viewed more favorably by DRC+ than wRC+. While we don’t know what specific park factors BP uses, Dickey-Stephens Park is infamously one of the toughest ballparks to hit at, in an otherwise fairly neutral Texas League.
• For DRC+, line drives are lovely, ground balls are grimy, and pop-ups are poison. Too many of the latter two help drag down Shed Long, John Andreoli, and Jaycob Brugman. Also, one in every three fly balls Jaycob Brugman hit was a home run, which wRC+ notes as impressive and DRC+ reads as some PCLunacy.
• ...Patrick Frick? We’ll have to check in on that as the 2019 14th rounder faces stiffer competition at higher levels next year.
• It’s not as stark as Arkansas, but High-A (A+) Modesto is one of the most tame offensive environments in the offense-happy California League. Both Cal Raleigh and Joe Rizzo in particular seem to have benefitted from park-adjustments.
• On the other hand, Modesto’s Keegan McGovern and Jack Larsen receive no such boost, and their Three-True-Outcomes heavy approaches reflect poorer in DRC+ than wRC+. Ditto for the already-struggling Miguel Perez in his first crack stateside.

Not too much is dramatically different in these metrics - there’s no player who looks terrible in one metric but great in another or vice-versa. Jake Fraley, Donnie Walton, and Evan White all clearly shine a bit brighter, while Shed Long looks less lustrous, but that’s about it. Julio Rodríguez is great in both, as is Jarred Kelenic. Kelby Tomlinson and Johnny Adams both had rough goes, no matter how you look at it. To cut the data a bit more palatably, here are all the players we included in our overarching prospect list post-draft, minus a few less notable names:

FanGraphs/Baseball Prospectus

No one metric is enough to measure a player’s quality, nor is it enough to evaluate what they will become. That makes having the biggest, most versatile toolkit handy all the more important. DRC+ makes for another neat screwdriver in the box.