Mark wants a number (5)
I believe the answer is:
score
I believe this clue is a double definition.
'mark' is the first definition.
(I know that mark can be written as score)
'a number' is the second definition.
(I know that score is a type of number)
'wants' acts as a link.
(Other definitions for score that I've seen before include "Number of goals/points" , "Keep count" , "Total of points" , "Tally in a game" , "Gain a point (20 of them?)" .)