This is for pro shops and customers alike.  Any mistake, freak accident, job that a shop operator swore to you was fine, etc. 

1. Get slug stuck halfway into ball.  I haven't had a ball split because of this before, but my boss has.

2. Forget to reset pitches before shaving top of slug off.  For those that don't know, there's always about 1/4 inch sticking out of the ball after you insert it that needs to be shaved down flush with the ball after drilling.  It's kind of a crescent shaped bit, used for shaving slugs and ball plug down, and it's shaped to fit the ball, so if you have the pitches at zero, it gets the slug or plug flush and even with the ball.  If you don't reset the pitches however . .

3. Ball plug doesn't set up.  Nearly impossible to clean up, super sticky, super thick, super tacky, just horrific stuff. 

4. Bit stuck in chuck.  The trick isn't getting the bit loose, it's getting the bit loose without stripping the grip on the chuck or really gouging it. 

Just a few to get you started, I don't want to share too many lol.

You just hope when you put the smile into the ball it's a plug job and not cutting a slug on a new ball.  Making the phone call that it will be another day is bad enough.

Lol, so I was drilling a ball for (thankfully) myself last season and for some stupid reason did opposite lateral pitches on the fingers. Oops.

Also, just a few weeks ago I had a plugged ball that for some reason didn't harden quite as well as it should have. It was relatively hard, as it wasn't quite liquid anymore when I cut it down...just a sticky mess and a re-plug lol.

Matt