Fool knocks out director in bar! That’s explosive stuff (5)

I believe the answer is:

nitro

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for nitro that I've seen before include "Explosive liquid" , "The whole universe" , "explosive material" .)

I've seen this clue in The Hindu.

Want a hint initially instead of a full solution? Install my app