O’Day has enjoyed more success against right-handed batters due to his arm angle, limiting them to a .246 wOBA over the past five seasons. That is 50 points below his wOBA against left-handed batters over the five-year span, but his 2013 splits were as drastic as Hunter’s. O’Day had a .207 wOBA against righties last season but a .384 against lefties. This is where Matusz came into play.
O'Day didn't struggle against lefties prior to 2013. I think the workload, plus less than stellar command, lead to the increase in his splits. An at bat that stands out was against James Loney at Camden Yards in April. O'Day left a fastball up and over, allowing Loney to homer to right-center. It was almost all about location, as the same 85 mph fastball retired numerous lefties in 2012. It just didn't get up and in enough on lefties, which was something that occurred more frequently in 2013.
O'Day also wasn't healthy the last month of the season, something that could have been bothering him much longer.