Swimming style (12)
I believe this is a double definition.
'swimming' is the first definition.
'style' is the second definition.
(I have seen 'Natant style' mean 'breaststroke' so perhaps 'style' could also mean 'breaststroke')
(Other definitions for breaststroke that I've seen before include "Adam Peaty's swimming style" , "What swimmers may do" , "Natant style" .)
'swimming style' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for backstroke that I've seen before include "Swimming style" , "action?" , "Way to move through water looking upwards" .)