Bat rolling is a process that can add 20-40 feet to a batted ball and Bat Shaving can add 30-60 feet to a batted ball. Bat rolling is accomplished by squeezing the bat’s barrel in between 2 hard plastic rollers or what is commonly called a bat rolling machine. Bat shaving is accomplished by placing the bat in a CNC lathe and removing some of the inner barrel material to make the walls thinner. Bat rolling is a less evasive process that normally does not mark or alter the bat in anyway other than the composite layers of material being broken down. Bat shaving on the other hand is clearly visible when you take off the end cap and look inside the barrel. The lathe tool will leave tiny groove marks where it has cut out composite material. Both methods are considered a bat alteration by almost any baseball, fast pitch, and softball association.
Bat rolling, however, is split on the morality of the practice. Bat rolling breaks in a bat as if you have hit about 400-800 balls. It is a known fact in the baseball, fast pitch, and softball communities that a composite bat gets “hotter” as it is used. There has also been a scientific study to prove this fact. So the debate is if bat rolling just accelerates the break in process why is it illegal? Should breaking in a glove be illegal also? Now back to bat shaving; bat shaving is without a doubt illegal in all associations and is definitely frowned upon. Bat shaving can make bats go over the certified stamp limit put on the bats by associations (most of the time the bat will either have to be rolled or naturally broke in to actually go over the limit). Some of these limits are put into terms of BPF or Bat Performance Factor. This is gauged by a ball launched at a great rate of speed, at a motionless bat. If the ball shoots off the bat 20% faster than it was discharged at the bat, then it surpasses the 1.20. Bat rolling has the potential to send a bat over the stated BPF stamp but so does the natural break in process. So bat both will increase the batted ball speed and both are illegal in almost all associations but bat rolling seems to be a more acceptable practice. Bat shaving will increase the distance far greater than bat rolling but the durability of the bat is diminished with shaving (about %50 less ball strikes as an average).