Second centre in rugby? (4)
I believe the answer is:
back
'second' is the definition.
(to second a motion is to back it)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for back that I've seen before include "Help!" , "part of the body" , "Support a play - player" , "bet" , "Rear; spine" .)