On April 29^th, while catching Joe Mauer took a Brayan Pena sharp foul ball off the inside part of his left knee. Up to that point, the seemingly healthy Mauer was hitting a robust .325/.419/.438. He had hit a home run, triple and four doubles in those 93 plate appearances. Since then, he has gone to hitting safely in just four of his last 31 at-bats (.129), including a gentle double and a ground ball that Mariners shortstop Brendan Ryan likely should have converted.

Now, many wonks will argue comparing 93 plate appearances to the outcome of another 36 plate appearances is the ultimate exercise in small sample size analysis. Additionally, the fact that he has faced a regiment of Jered Weaver (twice) and Felix Hernandez may lend credence to the notion that he is just slumping in May. However, because this performance drop-off started with the foul ball incident, it is hard to ignore the influence a shot to a load bearing limb may have on his swing. You have to wonder if Mauer is currently hurting more than he wants everyone to believe.

At the start of the season, Mauer was a line drive machine. In the season’s first month, nearly 30% of all balls off of his bat were hit on a line. So far this month, he has managed to hit just one line drive in 36 plate appearances since absorbing the Pena foul ball. The majority of his balls in play have been grounders.

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Without the assistance of the high percentage of line drives and the huge increase in ground balls, it is easy to see why Mauer’s numbers have taken a tumble.

Visually, through the monthly spray charts found at TexasLeaguers.com, we find that he has struggled to pull the ball in May as effectively as he did in April:

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Mauer’s left knee, the one Pena’s foul ball ricocheted off of, has been a source of pain for him in the past. In 2010, he had arthroscopic surgery after tissue inflammation experienced throughout the season. Last year, his bi-lateral leg weakness was concocted from what Mauer described as leg soreness from not properly working out his lower half following the 2010 arthroscopic surgery. If it was indeed re-aggravated, the left knee – the one he would pivot and drive off of during his swing – would keep him from pulling the ball with authority.

While the shot to the knee may be downplayed in the media, it would seem that the Twins have taken precautionary measures that would suggest that they are a bit more concerned about him. This month, manager Ron Gardenhire clearly recognized the need to alleviate the pressure on Mauer’s knees as since sitting out post-foul tip he has played nine games and only two behind the plate. Meanwhile, the front office, perhaps concerned over his resiliency, recalled Drew Butera from Rochester to serve as the third catcher in spite of a thin bench.

To Mauer’s credit, the majority of the ribbing last year appeared to be focused on his inability to work his way into the lineup and that his “bi-lateral” injuries were simply an excuse to avoid playing for a terrible team. This season, he’s played 30 of the 31 total contests, perhaps proving to his critics that he can play through the pain. Unfortunately, if he is in pain stemming from the foul ball, his performance has obviously taken a downturn.

Understandably, with Justin Morneau unable to play, the Twins are counting on their $23 Million Dollar Man to get out there and play. At the same time, if the team wants to ensure that he is available throughout the duration of the season, they may need to sit him a little more regularly than they have been doing up to this point.