Baseball's all time saves leader was injured Thursday shagging fly balls during batting practice in Kansas City. The New York Yankees' Mariano Rivera crumpled on the warning track after chasing a fly ball in obvious pain to a knee. He was carted off and taken to a local hospital for an MRI. The 42-year old Rivera has hinted this may be his last season before retirement. He has a 2.16 earned run average in 9 appearances so far this spring.