Stay calm to avoid sunburn (4,4,5,2)
I believe the answer is:
keep ones shirt on
'stay calm' is the definition.
(I've seen this before)
'to avoid sunburn' is the wordplay.
I cannot quite see how this works, but
'to' is found in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for keep ones shirt on that I've seen before include "Stay calm" , "Remain calm" , "refrain from post-match swap?" , "don't lose everything" .)