Jayson Nix is a career .220/.291/.362 hitter in the Major Leagues. That gives him a .653 OPS, a 75 OPS+, and a 73 wRC+. Even for a utility infielder, Nix has always been a poor hitter. We've seen him get the occasional big hit this year, but his bat hasn't earned him any playing time. Despite hitting just .256/.324/.311 this season, Joe Girardi is constantly putting him at the top of the lineup, earning him more at bats than he truly deserves. The announcers have tried to justify it since the beginning of May with a popular baseball narrative, saying that playing regularly has helped him finally start hitting. There are two parts to this myth, the first that Nix is playing regularly. This is easy to verify, as he's appeared in 54 of the Yankees' 63 games. In terms of plate appearances, Nix has 187 on the year, which is the sixth most on the team, behind Robinson Cano, Brett Gardner, Vernon Wells, Ichiro Suzuki, and Lyle Overbay. Nix is on pace for 481 plate appearances, the most he's ever had in his career, so the idea that he's seeing more playing time is very much confirmed.
The second part to this myth is more difficult to objectively measure, that regular playing time has helped him hit. You could measure his batting line every 10 games and see how the trends look.
Looking at the chart above, things look pretty good for this narrative. Nix has obviously started hitting much better as the year has progressed. In fact, over the last 14 games, in 53 plate appearances, Nix is batting .340/.392/.404 with 6 stolen bases. That's some ridiculous production out of your utility infielder. This sort of improvement is exactly what the Yankees need, and there's no wonder the announcers are getting us fans excited about having Nix in the lineup.
Except that Nix's .340 batting average over the last 14 games is only possible with a .485 BABIP. In fact, his entire 2013 batting average of just .256 is obtained through a .360 BABIP, a number nearly .100 points above his career BABIP. The reason for these abnormalities is a ridiculously high LD% in 2013 of 26.1, despite having a career 15.1 LD%. On top of that, Nix is batting .348 on ground balls in 2013, which is more than .050 points higher than his career .292 batting average on these batted balls.
What do these numbers mean? Nix's line drive rates and hits on ground balls are so ridiculously high that it would take a miracle for them to continue for even the best hitters in the league. Even his .256 batting average is a product of small sample size. Nix's high strike out rates are the main culprit to this low batting average, and it's the one thing that hasn't vastly changed from his career rates. As the plate appearances stack up, regression in his line drives and hits on ground balls should occur, bringing his batting average and on base percentage down.
Yes, things look bright at this point in the season, but the narrative assumes that he can keep it up because he's getting regular playing time. He's stacked up plate appearances and he's finally hitting, but we're only bringing up his ability to hit because he's finally run into some brilliant good luck over the last 53 plate appearances. A .485 BABIP won't continue, and not even his seasonal .360 BABIP will continue. Enjoy the hitting while he's hot, because there's not much more to this than small sample size.