It might be a boundary in sport (7)
I believe the answer is:
fencing
'sport' is the definition.
(I know that fencing is a type of combat sport)
'it might be a boundary in' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
'in' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for fencing that I've seen before include "enclosure" , "Olympic sport since 1896" , "Barrier; sport" , "Sport with swords" .)