The Story On xStats Outliers

Over the past few weeks I have been writing about xStats outliers, and to date I have covered Gary Sanchez, Trea Turner, and Jay Bruce. You may think Jay Bruce is the odd man out on that short list, but all three of these guys have big question marks around their power potential for different reasons, and you can read the three pieces for more information.  Today I want to focus on Trevor Story.

Trevor Story became a national sensation after he hit 7 home runs in his first 28 plate appearances, then hit 7 more over the course of the next few weeks.  Two months into his rookie season and the guy had 14 home runs, only nine shortstops hit more than 14 home runs through the whole of the 2015 season, three of whom had 15. His power persisted through the warm mid summer months, where he hit five home runs in June and eight more in July prior to suffering a season ending thumb injury on August 2nd.

Trevor Story hit 27 home runs, slugged .567, had a .272 batting average over the course of 415 plate appearances last season.  His power numbers have him ranked as the seventh best short stop – eighth if you count Trea Turner- and his ADP appears to have stabilized somewhere between 30 and 34.  Of course, you may ask, is this power sustainable?

When I wrote about Gary Sanchez I included a histogram depicting a rolling 20 BIP average of his exit velocities, and it created an interesting chart that showed how often he hit the ball in certain velocity ranges.  It tells you more than an average exit velocity would, I think, since in order to push up the higher end side of the histogram you need to pretty regularly hit the ball exceptionally hard.  Which is something Gary Sanchez had absolutely no problem doing in 2016.  He hit the ball 100+ mph on a fairly regular basis. Trevor Story hits the ball hard, too, not nearly to the same extent.  He doesn’t seem to have that sort of raw bat speed to produce exceptionally high exit velocities.  

Where Gary Sanchez compares favorably to Cespedes and Cruz, Story is more similar to Evan Longoria and Justin Smoak.  Yes, Longoria can hit his fair share of bombs, he hit 36 in 2016, but his quality of contact is significantly different than Cespedes or Stanton, for example. I mean, just look at these eight charts, I think they speak for themselves.

I have taken Trevor Story’s vertical launch angle, exit velocity, and batted ball distance information and compared it to the league average batted ball distances for balls hit with the same exit velocity and launch angle. Using this data, I found that Trevor Story has a Z-score around .11 for his batted ball distances.  I then went through and calculated the average batted ball distance for a major league home run, a Colorado Rocky batter home run, and for a home run hit in Coor’s field.

I then went through and, using the z-scores I calculated previously, found the likelihood of his balls travelling far enough to match these average distances. On average, his batted balls, if you assume a normal distribution for their distances, had a 8% chance of turning into home runs, on average, which translates to 5.2% of PA and 17.7% HR/FB. A far cry from the 23% HR/FB he put up in 2016, and just a touch higher than the 15% Evan Longoria put up 2016.

The home run rate I estimate for Story is significantly higher than Steamer and PECOTA; a bit above ZiPS; and below Davenport and ESPN.