Tardy in supporting round of applause (10)
I believe the answer is:
behindhand
'tardy' is the definition.
(thesaurus)
'supporting round of applause' is the wordplay.
'supporting' becomes 'behind' (I've seen this in another clue).
'round of applause' becomes 'hand' (as in a 'big hand', a round of applause).
'behind'+'hand'='BEHINDHAND'
'in' acts as a link.
(Other definitions for behindhand that I've seen before include "Late or slow in doing something" , "From which one might snigger" , "in debt" , "Late - in arrears" , "not keeping up with schedule" .)