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Statistical Breakdown of Diaz’s Defensive Impact

Aledmys Diaz will be a fine defensive shortstop in the future, but his errors could be costing the Cardinals in the playoff race this season.

At this point, Aledmys Diaz has to be in the Cardinals’ plans for the future. If he wasn’t at the start of the season, then he has certainly played his way into those plans by now. The only problem is that its unclear where he should fit in those plans. Ideally, Diaz would be the shortstop of the future and that would be all there is to it, but his defense has forced everyone to hold off on declaring him as such for now.

Diaz currently leads the major leagues with nine errors this season. You may already know that, but I certainly cringe every time I see that number. The only problem is that errors are not really a good indication of how good a fielder is. So how much, exactly, is Diaz’s presence in the field hurting the Cardinals?

So far, I count eleven runs that could have theoretically been prevented without Diaz’s errors (5 against the Angels, 3 against the Pirates over two games, and 3 against the Cubs). Statistically, that is on the higher side, as one error usually does not mean more than one run. However, that is the tangible result that Cardinals fans can point to when talking about the impact of the errors. With that being said, we have a few measurements that give us a better idea of what is happening.

The biggest problem with Diaz’ errors is that most of them have come on routine plays. Those hurt more than errors on plays that are more difficult because the batter is expected to be out. In other words, if Diaz makes an error on a play that the average shortstop makes 95 percent of the time, then he is giving away more expected outs than he would if the average shortstop only makes that play 50 percent of the time.

Without getting into the mathematical derivation of these numbers, an error typically costs a team somewhere around one-half of a run, and getting to ten runs means that you are roughly costing your team one full win. In other words, if we take context out of the equation, then Diaz has cost the Cardinals about four runs with his errors this year.

Fangraphs’ advanced fielding metrics say that Diaz has cost the Cardinals 2.3 more runs than the average shortstop has cost his team so far this year. That’s probably about right if we assume that all of Diaz’s errors have been an average error (the average shortstop does not have 0 errors). But as we noted before, Diaz is not making average errors; he’s making routine errors. Given the expected outs that he has cost the Cardinals’ pitching staff, he has probably cost the team somewhere in the 3-3.5 runs below average range.

If we prorate his current numbers to 162 games, then we are now talking about 1-1.5 wins lost just due to his errors. That number may seem low, and many would argue that he has cost the team that much with the nine errors that he has already committed. However, that would be enough to wipe out everything that he has done at the plate in the first quarter of the season. So far, Diaz has provided approximately 1-1.5 wins on offense, according to Fangraphs’ offensive runs above average numbers.

On the whole, Diaz still rates as an average defensive player. His range and the fact that he plays shortstop makes up for all of his errors according to most defensive wins or defensive runs metrics. Nonetheless, he still needs to take care of his errors problem. 1.5 wins may not seem like much, but it will make a huge difference when the National League Central has three teams trying to win the division and wild cards spots in September.

Errors tend to be a problem for young players early on, so I wouldn’t worry about this too much long-term. In fact, I think it is fair to say that he will make a fine defensive shortstop in the future. The Cardinals want to win now, though. One way to pick up a win without changing the roster would be to fix Diaz’s problem with routine ground balls. There is still time to turn the errors problem around this season, and that could make a big difference in the remaining 120 games.

Photo captured by Jeff Curry- USA Today Sports