Projection: all but one in football team active (5)
I believe the answer is:
tenon
'projection' is the definition.
(I know that tenon is a type of projection)
'all but one in football team active' is the wordplay.
'all but one in football team' becomes 'ten' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'active' becomes 'on' (I've seen this in other clues).
'ten'+'on'='TENON'
Can you help me to learn more?
(Other definitions for tenon that I've seen before include "Part of joint that fits in mortise" , "Tongue of wood for joint" , "Mortise filler" , "Wood fitting into a mortise" , "Connection" .)