Let me start by saying that this post is not the least bit inspired by Anthony Rizzo's 3 strikeouts in 6 plate appearances vs lefties this season. It's 6 plate appearances. That's it. This is something I've been meaning to write since the 2012 season ended and I'm just finally getting around to it.
We all know Anthony Rizzo had a rough debut season in 2011 with the Padres. We all know he had a pretty good first season with the Cubs last year. We can probably guess that he was terrible vs lefties in 2011 because he wasn't very good overall. We'd also probably guess that he was better vs lefties last season. We'd be wrong.
In 2011 Rizzo had only 33 PA vs lefties (appears he was given days off when lefties were on the mound) and he hit .172/.273/.345. That's a .279 wOBA and an 80 wRC+. In 2012 Rizzo had more than 100 plate appearances against lefties and hit .208/.243/.356. His wOBA was .260 and his wRC+ was 56. He was 12th worst in baseball in wRC+ vs lefties last season.
CAIRO projects a .321 wOBA vs lefties this season, which is average to slightly below average. As a 1st basemen, it's not at all good since the average 1B is going to have a much higher than average wOBA. Only 15 1st basemen, out of 41, who had 100 plate appearances vs lefties last year had a wRC+ below average (under 100). Rizzo's was 4th worst, better than only Carlos Lee, Ike Davis and Justin Morneau).
So far in his young career, Anthony Rizzo has only 146 plate appearances vs lefties. His 61 wRC+ is pretty bad. I don't think it's time to even start thinking about platooning the guy. Certainly not when the Cubs aren't expecting to contend.
He's still young and should improve, but it is something to watch. Some batters struggle vs same-handed pitchers. Rizzo could be one of those guys. I'm hoping we'll see his numbers vs lefties regress towards his numbers vs righties, but there is no guarantee it's going to be any good.