The phrase "best pitcher" refers to the player in baseball who is considered the most skilled at throwing the ball accurately and effectively to the batter. Full definition
And he's considered a pretty good pitcher by today's standards. (si.com)
He's been a very good pitcher that we would miss. (sbnation.com)
Reminds me of how the Astros told Verlander last year to drop his release point to where it was earlier in his career (he didn't know it was different), and he has been the 4th - best pitcher in baseball (by wOBA) since that day (Sept 5, 2017). (sbnation.com)