Player reacts when beaten by striker's header (7)
I believe the answer is:
actress
'player' is the definition.
(actress is a kind of player)
'reacts when beaten by striker's header' is the wordplay.
I cannot really see how this works, but
an anagram of 'reacts' is 'actres' which is located in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for actress that I've seen before include "One on stage" , "Casters (anag.)" , "Female player" , "one with a particular role?" , "One playing" .)