Mariano Rivera may have thrown his last pitch for the Yankees. Photo: © Anthony Gruppuso-US PRESSWIRE

Mariano Rivera appeared to seriously injure his leg Thursday night shagging fly balls in Kansas City:

The bad news on Mariano Rivera from Joe Girardi: “It appears that he has a torn ACL. He will obviously go back to New York and be examined by our guys.” If this initial diagnosis holds true, Rivera will likely be out for at least 6-8 months. Rivera had hinted that 2012 would be his final season, but he had also said he wanted to go out on his terms. We’ll see what this means for his future.

Rivera, speaking through tears in the clubhouse, talked of his injury and future. He said he caught his spike between the grass and dirt and could not pull himself up. He injured his ACL and meniscus. “It’s more mentally than physically,” he said. “I let the team down.”

The Yanks’ closer injured himself in the outfield during batting practice but said he had no regrets. “If I had to do it over again, I’d do it over again,” he said of shagging in the outfield.

This would be a sad way to end Rivera’s career. I thought he could pitch until he was 50, and while he hinted of retirement, I suspect the joy of competition that exists in that group of Yankees who came up together in the middle 1990s might keep Mariano in the game. Now a leg, internally mangled from knee to ankle, will likely end his career.

Just how good was Mo? Look at his career from the point of view of the batters against him. His rookie year (when he started) is nothing great, but since moving to the bullpen in 1996:

1. The highest batting average against Rivera in a season is .248. In six seasons his final number came in under .200.
2. The highest OBP allowed is .294. A hitter with 200 PA and a .294 OBP would likely get sent to the minors.
3. The highest slugging percentage he allowed was .350. In other words, his highest slugging percentage allowed in a season was no better than a decent OBP. All these highs were set in 2007.
4. Since setting those career highs, batters faced Mariano 1011 times. Their slash line against him stands at .190/.228/.272.

Look at the batting lines by year again. Mo faces batters between 200 and 300 times a season, making each season a small sample size. In all that time, with all those small sample sizes, he might have posted one bad season. It just didn’t happen. By throwing one pitch well and fastidiously staying away from the middle of the plate, Rivera was not just consistent, but consistently great. Even if his 2008-2011 OBP started rising 10% a year, he still would have been effective for another three or four seasons. He will be missed.

Meanwhile, the Yankees need to fill the hole in the pen:

While speaking with reporters after the game, Girardi spoke about the current state of the bullpen. “You lose a Hall of Famer. That changes it a lot,” he said “If that’s what it is, that’s about as bad as it gets.” Either David Robertson or Rafael Soriano could fill in, and Girardi said he was going to sleep on this decision. Considering how Girardi uses the closer, I’d rather see Soriano take the 9th inning and Robertson stay in the fireman role. They can’t really go wrong with either though.

It does become more important now to get the rotation in shape. While closing games won’t be a problem, Yankees starters have not gone deep in games. With one less stellar reliever, the Yankees can’t count on turning contests into six inning games.