MLB Starter Wins Chart – Edge around 19
Although there is always the possibility that my observation is nothing more than regular variance, raw data suggests emotional factors coming into play for a pitcher going for, having, and having past 20 wins. Quite the achievement. The simple thought is this: players put the effort into getting to the milestone (+24 units at 19 wins and a 61.2% win rate). Once they have acheived the feat, they take a breather: -36.9 units at 20 wins and a 52.5% wins rate.
As for why a pitcher would struggle the worst at 18 wins…you are welcome to leave a comment. My assumption is two things: 1. Again this is all regular variance (probably the best assumption). 2. 15+ starter wins is already a feat in itself, and this typically correlates with expensive bets on clinched playoffs teams or teams with 99.9% probability for playoffs who usually stop playing as hard for streaks (and in general).
RAW DATA PROVIDED BY WWW.SPORTSDATABASE.COM
To run a query for this on your own click here: http://killersports.com/mlb.py/query?text=starter%20wins&sort=query_header&sid=guest_005360
or type: "starter wins" as SDQL text….