Maybe watching international display (6)
I believe the answer is:
attest
'display' is the definition.
(thesaurus)
'maybe watching international' is the wordplay.
I cannot really see how this works, but
'watching' could be 'at' (e.g. watching a tennis match means you are at it) and 'at' is present in the answer.
'international' could be 'test' (as in a test match in cricket) and 'test' is found within the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for attest that I've seen before include "say, in court" , "Adjure" , "Act as witness" , "Verify" , "Demonstrate" .)