사전에서 따 왔습니다.
If you do something on the fly, you do it quickly while something else is happening, and without thinking about it very much.
우리가 사용하는 한 큐(one cue)이나 한 방(one shot)하고는 조금 다른다는 느낌입니다.
One cue is enough to win a billiard game. One shot is enough to kill them all.