Player needing room is first to tackle (7)
I believe the answer is:
cellist
'player' is the definition.
(cellist is a kind of player)
'room is first to tackle' is the wordplay.
'room' becomes 'cell' (cell is a kind of room).
'first to' indicates taking the first letters.
The first letter of 'tackle' is 't'.
'cell'+'is'+'t'='CELLIST'
'needing' is the link.
(Other definitions for cellist that I've seen before include "Musician in string section" , "E.g. Casals, du Pre" , "String player" , "Lloyd Webber?" , "Du Pre or Lloyd Weber" .)