Is Bobby exhausted by it? (4)
I believe the answer is:
beat
'it?' is the definition.
I can't judge whether this defines the answer.
'is bobby exhausted by' is the wordplay.
I cannot really see how this works, but
'is' could be 'be' and 'be' is found within the answer.
'by' could be 'at' and 'at' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for beat that I've seen before include "Rhythm, stir vigorously" , "Tan" , "Rhythmic musical unit" , "See 22" , "Defeat; pulsate" .)