Biologist atop swaying tree - one may be out on the field (9)
I believe the answer is:
cricketer
'one may be out on the field' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for cricketer that I've seen before include "Point one may be at" , "Don Bradman or David Gower, say" , "Sportsman who bats or bowls" , "Player of traditional English game" , "Paul Stirling or William Porterfield, say" .)