Sinker velocity sink?

Another time, I drafted Alex Wood in my fantasy team. Last time, I drafted him in ESPN fantasy in 2017, it was his all-star season, and I won in the league. In 2017, he earned 16 wins with ERA only 2.72. In 152.1 innings of work, he threw 151 strikeouts. Before the all-star game, his record was 10-0 with ERA 1.67. However, he only had 6-3 with ERA 3.89 post all-star. Batting average against him jumped to .262 from .174. Why did this happen?

 Alex Wood’s delivery is very unique in the league and he relies on his sinker. Looking back at his sinker velocity year by year since he made his MLB debut in 2013, we can see that the velocity usually dropped in the second half. So we go deep to see the numbers every year.

Alex Wood made his MLB debut in May 2013, he pitched 31 games (11 starts), in total he pitched 77.2 innings. His average sinker velocity dropped gradually every month. In June 2013, the average velocity was 93.5 mph, while in August, the average velocity was 91.8 mph.

Month (2014)	Apr.	May	Jun.	Jul.	Aug.	Sep.
BAA (Sinker)	.267	.282	.200	.333	.184	.222

Wood started 24 games and had 11 relief appearances in 2014, he finished the season with ERA 2.78, ranked 15th lowest in the league. His sinker velocity remained around 90 to 91, but dropped to around 88 to 89 in July. From April to June, he already pitched 73.1 innings, very close to his total innings pitched in 2013.

Month (2015)	Apr.	May	Jun.	Jul.	Aug.	Sep.
BAA (Sinker)	.299	.357	.305	.242	.228	.274

Wood started 32 games in 2015, 20 games with the Braves and 12 games with the Dodgers. His average sinker velocity was 89.8mph and BBA was .285. His sinker was not that effective in 2015.

Due to injury, Wood only pitched 60.1 innings in 2016.

Month (2017)	Apr.	May	Jun.	Jul.	Aug.	Sep.
BAA (Sinker)	.161	.233	.195	.311	.300	.306

2017 was a breakout season for Alex Wood. His sinker was dominant in the first three months. From April to June, he pitched 73.2 innings, hitters only bat .200 against his sinker. His sinker velocity was between 92 and 94. As we can see his sinker velocity went down gradually, hitters were more comfortable at hitting his sinker.  

Month (2018)	Apr.	May	Jun.	Jul.	Aug.	Sep.
BAA (Sinker)	.233	.256	.351	.270	.263	.000

Wood’s sinker velocity (average) was 89.9 mph in 2018. He made 27 starts and then was moved to the bullpen after Sep. 10. From March to June, Alex Wood pitched 87.2 innings.

Wood only pitched 35.2 innings in 2019. Back injury caused him to miss the first-half of the season.

Alex Wood’s delivery is so unique and it takes lots of efforts. As we can see the numbers in the previous seasons, his sinker velocity usually dropped after 70 or 80 innings pitched in the season. If baseball does return this season, I am wondering if he needs some extra days off after pitching 70 or 80 innings, thus this may help him pitch more consistently in a long season. Meanwhile, if his sinker velocity could reach to 92-93 mph, it would definitely be great news for the Dodgers and fantasy owners.