MLB trade deadline: Is Gerardo Parra still good at defense?

A glance at a list of the worst defensive players in baseball so far in 2015, according to Fangraphs, reveals many of the expected suspects. There are a few designated hitters miscast as position players, such as Nelson Cruz, Prince Fielder, and Pedro Alvarez. You’ll find injury casualties, such as Matt Kemp, and historically immobile defenders, like Chris Colabello. And of course, the Red Sox disastrous defensive duo of Hanley Ramirez and Pablo Sandoval, each well on his way to the worst defensive season of his career, is present as well.

There is, seemingly, one misfit on the list: Gerardo Parra, a 2013 National League Gold Glove winner in right field. According to Ultimate Zone Rating (UZR), Parra has been worth a little over 50 runs above average defensively during his career. UZR divides the field into zones, and breaks down the likelihood that a play in a certain zone will be made given the batted ball characteristics and game situation. By comparison, the two players directly preceding Parra, Prince Fielder and Pedro Alvarez, have been worth -47.7 runs and -29.2 runs in their respective careers, according to UZR. In 2013 alone, when Parra won his Gold Glove, he was worth 31.1 runs according to UZR. However, this season, Parra has already cost his team 9.8 runs defensively.

What could have changed so drastically that, in just a year and a half, Parra has gone from being rated the best fielder at his position to one of the worst? While he was unspectacular in 2014, Parra still rated as roughly a league-average fielder. The erstwhile Diamondback turned 28 earlier this year, so it is unlikely that age is playing a serious role in his perceived decline. Reports suggest that Parra has not been suffering from any sort of injury either, so while it is possible that something nagging has flown under the radar, it does not seem like health has had a major effect on his defensive performance. In fact, Parra has been 34 percent better than league average offensively, so the rest of his game appears to be firing on all cylinders.

A closer look at the plays which Parra has struggled with sheds some light on his struggles, and on a potential rebound. Inside Edge fielding data divides defensive plays into six categories: Impossible (plays which are made 0 percent of the time), Remote (1-10 percent), Unlikely (10-40 percent), Even (40-60 percent), Likely (60-90 percent), and Routine (90-100 percent). Parra’s success rate on impossible plays has been 0 percent, obviously, and his rate on routine balls has been 100 percent. So his issues have stemmed entirely from plays in the middle four categories. The following chart shows FanGraphs data and displays his percentages in each category, comparing 2012-2014 against this season, with the number of opportunities in parentheses.

Parra is actually besting his career average of about 15 percent on remote plays, converting them at 20 percent. And on likely plays, Parra has been converting 86 percent this season, which is exactly in line with his career average. Parra has only fielded three balls classified as even this season, converting two. While this technically puts him below his career average, the sample size is too small to have much of an effect, as one more successfully converted play could put his percentage on even plays back above his usual average.

The issue with Parra’s fielding this season, it turns out, has occurred almost entirely on balls classified as unlikely. Plays in this category are usually made between 10 and 40 percent of the time. His career average (dating back to 2012) on these plays, coming into this season, was just over 41 percent, accrued over 34 chances. This season, on 6 opportunities, Parra has yet to successfully convert an unlikely play. In the past, Parra was one of baseball’s premier players on unlikely plays, and this year, he has been tied for its worst.

Of course, small sample bias occurs here, and that is the point. So much randomness can occur on a sample of 6 plays, especially for an outfielder like Parra. While it is plausible that Parra has lost a step over the years, it is virtually impossible that one of his trademark skills, converting unlikely plays in the field, has eroded entirely. The expectation is that, as the sample size increases, so will Parra’s conversion rate. He may never return to his Gold Glove heights of 2013, but it is feasible that Parra plays at an above-average level on the defensive side for the second half of the season.

He may not, however, do so for the Brewers. Parra is having the best offensive season of his career, posting an ISO of .199 through his first 316 at-bats. His slugging percentage sits at .514, 18^th in the majors among qualified hitters. He has always hit righties hard, but this year, Parra has even dented lefties at a rate 27 percent better than league average. As he is signed cheaply through the end of 2015, Parra serves as an excellent midseason rental for a contender. Potential buyers could be the Mets, currently 28^th in the majors in wRC+ (a measure of park-adjusted offense) as a team, or the Royals, who recently lost Alex Gordon for 8 weeks and could make use of a good left-handed bat. For Milwaukee, one of only 3 or 4 true sellers, trading Parra would be a good way to recoup some value for an asset who likely will not help their next winning team.

With a career ISO of .128, it is unlikely that Parra will sustain his outburst in power. However, positive regression in his fielding stats – specifically those on unlikely plays – may offset the negative offensive regression that seems to be coming. For this reason, Parra still projects to be an excellent rental for a contending team in need of an outfielder.

This is Tom's first post at Beyond the Box Score. He can be found on Twitter @Od_tommy.