When the Braves signed Julio Teheran to an extension two years ago, the team and Teheran likely did not expect his 2015 struggles. A 4.04 ERA / 4.40 FIP / 4.19 xFIP left something to be desired for Atlanta's de facto staff ace. Shawn Brody chronicled his struggles against lefties on this site, while his shift away from high pitches was also detailed here by Murphy Powell. Investigating the cause of Teheran's struggles has been the focus of analysis of the pitcher.
However, there were times when Teheran looked exactly like the pitcher the Braves were hoping he would become. On July 22nd against the Dodgers, Teheran had essentially his best start of 2015. This is arguable, but here's why: It was tied with his 5/21 start for best single-game FIP at 1.28, and it was his best single-game xFIP at 1.70. He struck out 11 batters, his highest and only double-digit total of 2015. Coincidentally, his previous double-digit strikeout game was almost exactly one year prior, on 7/21/2014 against the Marlins.
Teheran went seven innings and gave up three runs on six hits, with three walks, and 11 strikeouts. He began the game on a tear; Joc Pederson, Howie Kendrick, Adrian Gonzalez, and Andre Ethier, the Dodgers' first four batters, all struck out swinging. Carl Crawford struck out swinging for the next out, and Yasmani Grandal got picked off. The strikeouts continued in the third as Teheran struck out opposing pitcher Mike Bolsinger and Pederson again. Things came unhinged in the fifth inning as he gave up three runs, but he got two more strikeouts that inning. Teheran clearly had something working in this start.
He may have been doing something in this start that he neglected to do in any other start last season.
Teheran ended the year with a 40 percent ground-ball rate, but he induced a 53.8 percent GB rate in this game. Granted, that did not matter much given 11 strikeouts and 21 total outs (including a pickoff) but that ground-ball rate was his third-highest in a game in 2015. He achieved that rate while throwing his four-seam fastball more than in any other start all season.
According to Brooks Baseball, Teheran threw his fastball about 42 percent of the time in 2015. Against the Dodgers, Teheran pumped it in there 64 percent of the time, which was the highest rate of any game last season. In fact, Teheran hadn't thrown his four-seam fastball that much in a single game since 2012. Despite the increased ground-ball rate, Teheran did not in fact keep the ball down.
Recall that Powell's article was about Teheran's shift down in the strike zone. Contrast that with the following four-seam fastball zone plot:
Sure, he threw a few pitches low, but that is not the zone plot of a pitcher throwing pitches low and away. Teheran painted the corner with his fastball to get ahead of hitters (though the Dodgers were chippy about the strike zone). With the Dodger hitters taking the fastball early in counts, Teheran was free to pump his fastball in high or bury his slider in two-strike counts. That's exactly what he did.
In 2015, Teheran continued to keep his four-seam fastball up in the zone. As mentioned earlier, he threw his fastball much more during this July start than any other game. Hitters were seemingly unprepared for it; though Teheran allowed 46.2 percent hard contact in that game, 76.9 percent of all contact was pulled. Combined with the ground-ball rate, hitters were either striking out or rolling stuff over to the right side of the infield.
What this game suggests is that Teheran should loop his four-seam fastball back into his usage patterns. On the other hand, decreasing velocity as the aging process begins suggests that Teheran has to figure out a way to pitch without his four seamer being the bread and butter. However, that's not what Teheran did as the season wore on. Below, I've plotted Teheran's four-seam fastball usage from Brooks Baseball on a game-by-game basis in 2015 and added a trend line in Excel.
The R^2 is at only about 0.3, but there is a trend up through the season. If increased usage of his four-seam fastball would lead to better results, as suggested by the 7/22 game, then theoretically Teheran's second-half splits should be better than his first-half splits (though the halving is arbitrary, it works well enough here).
First half: 4.56 ERA / 4.71 FIP / 4.33 xFIP / .338 wOBA allowed
Second half: 3.42 ERA / 4.05 FIP / 4.02 xFIP / .302 wOBA allowed
Teheran's second-half strikeout rate and home-run rate were big improvements over the first half. There is some definite correlation here, but I'm still hesitant to give any causation. Teheran's first-half line drive rate and HR/FB rate suggested regression, and it's possible that is exactly what it was. It's also possible that Teheran rediscovered his fastball. Regardless of which it is, Teheran is going to have to learn how to get batters out now and later, whether he can rely on his fastball or not.