I was glancing at the pitch by pitch for a game today and saw NF (Nasty Factor) in addition to a description (fastball, slider, etc.) and miles per hour (mph). I can't find the balloon definition but it seemed interesting.
For the few minutes I followed the game this way it helped me see what the previous batter had done, which I missed because I was so bored I was doing other stuff, like watching the 1972 movie 1776. Hey, I'm a real American.