Data via Baseball Savant
The most common balls in play come off the bat at 85-100 mph, but exit speeds in 2015 have ranged from 30-119 mph, according to MLBAM data compiled by Baseball Savant. (Data excludes bunts and approximately 40% of batted balls for which speed was unavailable.) Not surprisingly, harder-hit balls are more successful; 59% of balls at 100+ mph became hits, compared to just 21% of balls at 75 mph and slower. There are also a few errors in the raw data, such as this Mike Trout homer, which was recorded at a mere 48 mph.