How often are bats already "broken" before hitters know it?

[Blitz Dorsey]

There must be times when a bat is somewhat cracked and a player doesn't know it. And that obviously would affect how hard/far they could hit the ball. I'm sure it doesn't happen very much, but I have no doubts that occasionally their wooden bats are already cracked to some extent before they even go up to the plate. I just wonder how many times it happens. Again, probably not many, but has anyone else ever wondered about this?

It's one thing when a player gets sawed off and breaks his bat. Or even hits it on the end of the bat and shaves it to some extent. But I've seen far too many times where a player appears to hit the ball on the sweet spot, but still breaks his bat. Some of those bats must already be broken (barely cracked) and the hitter doesn't know it.

[Johnny Footstool]

Hitters tap their bats on the ground in the on-deck circle. If there is a significant break, they can usually feel the difference in vibration. Still, I bet it's not uncommon for them to bat with a slightly-cracked stick.