Royals coach Rusty Kuntz is an underrated asset

When I attended FanFest this year, I asked Terrance Gore about how he prepares himself to steal a base when he pinch-runs. It's a situation in which everyone expects a steal, so I figured the answer could be illuminating. Gore referenced Rusty Kuntz in his answer as someone who has helped him become a better baserunner. "Let your eyes move your feet" is what Gore said Kuntz told him.

It's not just teaching the runners what to do, though. Kuntz scouts opposing pitchers extensively. From a Sporting News article:

"Rusty is our guy," ALCS MVP Lorenzo Cain told Sporting News. "He’s the guy who finds the other guy’s weaknesses on the mound. (The pitcher) might do something with his head, his arm or shoulder or whatever the case may be. He finds it, and definitely relays it to all his basestealers."

From a Boston Globe article in 2014 ranking the best coaches in various roles:

Outfield/base running

Rusty Kuntz, Royals — Kuntz’s outfielders are fundamentally sound and get great jumps on balls. Kuntz has been able to improve arm accuracy.

So Kuntz is not only a base running asset, but also an outfield asset. This came into play with Alex Gordon. Gordon has a mechanical pregame routine. He shags fly balls like he would during the game; he works out meticulously. However, before he became Danger Ox, Gordon had to start somewhere. This is where Kuntz comes in. This great story details Gordon's journey and some of his experience with Kuntz.

How do you stay behind a fly ball so you're coming in? Answer: "You look at the top of the ball."

On a line drive, how do you know if it's in front of me or behind me? "The bill of the hat," Kuntz said. "If it stays under the bill, you know it's at you or in. If your head goes up, then you know you have to go back."

How do you keep your body from bouncing? "Open your mouth. That relaxes your jaw, which relaxes your shoulders, which relaxes your body."

There were plenty of articles written about Kuntz's skill in this area. I simply wanted to remind you of the outside opinions of Kuntz. Those were a lot of words. Not a lot of data. I'll present to you some data. For the more prolific base stealers of 2014, here are their stolen base success rates with Kuntz as first base coach and without. Kuntz took over first base coaching duties on August 4th, 2012. Alex Gordon is the only guy who was there for Kuntz's first go-round at first base coach (2008 and 2009 seasons).

It's a bit of a mixed bag. Escobar and Gordon vastly improved with Kuntz as their first base coach. The other three have small differences. In order to figure out if these differences were significant or not, I turned to the Chi Square test. There are different sample sizes with and without Kuntz; this technique can take care of that by comparing the actual stolen base and caught stealing numbers with expected numbers. I used the "with Kuntz" rate as the expected rate to calculated expected stolen base and caught stealing numbers using the sample size from the "without Kuntz" group.

If I screwed up a Chi Square test, please, just revoke my privileges now. It's one of the first techniques learned in statistical testing, and I haven't used it in a long time.

Cain, Dyson, and Aoki's rates with Kuntz as coach are not significantly different from their rates without Kuntz. In Dyson and Aoki's cases, the rates were just not very different to start with. In Cain's case, the sample size without Kuntz is too small for that roughly 9 percentage point difference to mean anything. However, Escobar and Gordon's rate differences were both significant.

It's possible that experience in the league is responsible for improving their rates. I hesitate to accept this conclusion for two reasons. First, speed is something that's supposed to decline as a player ages. Stolen base rates theoretically should not improve as a player gets older. Unless, you know, the player gets better at reading the pitcher and timing and so forth, which is what Rusty Kuntz is there for. Second, Terrance Gore, an inexperienced major leaguer, was able to steal bases relatively easily despite everyone knowing what he was there to do. Obviously, Gore is a very fast runner, but Gore noted that Kuntz was able to pick him off very easily. Kuntz supposedly taught him to avoid this, so Kuntz helped Gore compensate for his lack of experience.

I pooled the 5 players' numbers together to perform another Chi Square test with a larger sample size. As a group, those 5 players had a stolen base success rate of 83.2% with Kuntz and a 75.4% rate without. Because the sample sizes are larger, this is actually a significant difference. So, let's say that Kuntz is responsible for about an 8% increase in stolen base success rate. Can this translate to runs? Yes, I believe so, using the wSB formula. This will be an estimate, so put some error bars around the run value. Also, remember, I'm looking at only 5 players. Not the whole team*. In the wSB formula, I'm using 2014 constants despite having data from other years, so that's another limitation.

*I considered comparing team years with Kuntz to team years without Kuntz, but that introduces the confounding factor of different players. The analysis would be moot.

To estimate the run value, I'll calculate the wSB using the 75.4% stolen base success rate without Kuntz for those 5 players, and then I'll compare that to the wSB using the 83.2% with Kuntz. I'll divide the difference by 10 to get an estimate of how many wins Kuntz has helped the Royals get during his tenure as first base coach. Pinch running confounds this analysis due to different players getting on base for the base stealer, so add even larger error bars.

wSB of those 5 players with Rusty Kuntz (8/4/2012-present + 2008-2009 for Gordon): 26

Expected wSB of those 5 players without Kuntz over the same time period: 12

According to this analysis, Kuntz's base running instruction on stolen bases to only those 5 players was worth 1.4 wins above replacement. That's roughly 0.11 wins per player-season (the 2012 mid-season promotion complicates things. There were about 13 player-seasons under Kuntz's tutelage). So, for those 5 players, that's roughly half a win per baseball season.

I'd peg Rusty Kuntz's base running instruction to be worth somewhere around 0.5-1.0 wins above "replacement coach" each season depending on how much the team steals. That's not including his outfield instruction or any other base running instruction. I don't have the data to do a similar analysis for outfield defense; StatCast data pre- and post-Kuntz would give me these data, but that's never going to happen. We'll have to be content with the narrative the Kuntz was instrumental in Gordon's career turnaround as well as the current prowess of the outfield defense.

Kuntz has a long history in baseball. He was a player for the 1984 World Series champion Tigers. He has never been a manager of a team, but I bet the Royals are happy to have him. He's excellent in his role, and I hope he stays for as long as he can.