Lance Lynn has surprised everyone this season. He now ranks 9th on the MLB list of qualified starters by K%. I don't think that was on anyone's list of expected outcomes. Now, Lynn has pitched less than half a season, but he's faced 329 batters, which means he's reached a point where many peripherals have already stabilized: strikeout rate and groundball rate.
I had thought at first to compare Lance Lynn to another Cardinals prospect who started out relieving on a World Series-winning team. I was surprised to find how much Lynn's partial 2012 exceeds Adam Wainwright's 2007. Lynn has a 26.2% K rate and an 8.2% walk rate. He has a 2.89 FIP and a 3.26 xFIP, as well as a 3.08 SIERA. He's allowing 49.3% of all balls in play on the ground.
Adam Wainwright's first season as a starter was less impressive. He had a 15.4% K rate and a 7.9% walk rate. He had a 3.90 FIP, 4.45 xFIP, and a 4.58 SIERA. He drew groundballs at a 48.2% rate. In fact, Wainwright has never struck out batters at a rate comparable to Lynn's current K rate over a full season. His career high was 23.4% in 2010. Wainwright wouldn't have a comparable season by his general peripherals until 2009 (3.11 FIP, 3.32 xFIP, 3.47 SIERA).
Wainwright's debut as a starter doesn't come close to Lynn's partial season. And he doesn't strike out batters at the same rate as Lynn has in his partial season.
In searching for a good comp, I looked for pitchers with great K rates and average to slightly above average walk rates. Most of the best pitchers have very low walk rates. But a few excellent pitchers, like Max Scherzer or Gio Gonzalez, strike out a lot of guys but allow a lot of walks. But even those pitchers didn't look this sharp in their debuts as starters. Gonzalez has long struggled with walks, striking out batters at a 24% rate in 2009 while walking opponents at a 15.3% rate, with an overall 4.47 FIP in a 20-start season.
A comp I like a little better is Max Scherzer who started 30 games for the Diamondbacks in 2009. He struck out batters at a 23.5% rate and walked them at an 8.5% rate, with a 3.87 FIP. That's still understating Lynn's progress so far, although we should certainly expect that his K and BB rates will decline somewhat.
Lynn has been worth 2.0 WAR so far this year, and his debut suggests he could be a regular 3-4 WAR pitcher, like Scherzer. Not many pitchers, even ones that become all-stars come out of the blocks the way Lynn has.