I think the short answer would be; you, the baseball and the baseball bat would be vapourized! My math is a bit rusty, but think the energy released would be in the order of 1000 times the Hiroshima bomb!
I wouldn't wanna TRY to find out!
Traveling at even one tenth the speed of light there's no way you would ever see it coming.
Regardless, I'm in Trevor's camp as far as the probable outcome if you were to actually HIT the ball!
'Still theorizing regarding a near miss...