Needing to go at once, way to get out direct (6)
'needing to go at once' is the definition.
(to be caught short is to need to urinate)
'way to get out direct' is the wordplay.
'way to get out' becomes 'caught' (catching is a way to get a player out in cricket).
'direct' becomes 'short'.
'caught'+'short'='CAUGHT SHORT'
'direct' is the definition.
The answer and definition are different parts of speech. However, past participle verbs and adjectives sometimes define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for caught that I've seen before include "Ensnared" , "Seized" , "Came upon" , "Stopped and held a moving object" , "Trapped or arrested" .)