1. a lesser form of "be back later" but a longer time period than "be right back" because brb
suggests you'll be gone a short period of time, while bbl
suggest you'll be away for an extended period of unknown time. bball is perfect for those "in the middle" situations
2. or bball could mean basketball or to play basketball
1. i was only going to be gone for a couple hours so i put an away message of "b.b.a.l.l."
2. yo dave, lets bball down at the courts