Occasion for players to get their heads down (5)
I believe the answer is:
scrum
'down' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for scrum that I've seen before include "Melee" , "Forwards at rugby union" , "Disorderly struggle" , "A pushy rugby formation" , "brawl" .)