Force a beat to calm down (5)
I believe the answer is:
abate
'to calm down' is the definition.
(I've seen this in another clue)
'force a beat' is the wordplay.
'force' indicates anagramming the letters (letters must be forced into a new order).
'a'+'beat'='abeat'
'abeat' anagrammed gives 'ABATE'.
(Other definitions for abate that I've seen before include "Relax" , "Reduce" , "Become less in intensity" , "Go down like storm" , "Lessen in intensity" .)