In sport, an offside position? (5)
I believe the answer is:
point
'offside position?' is the definition.
'point' can be an answer for 'position?' (thesaurus). I am unsure of the 'offside' bit.
'in sport an' is the wordplay.
'in' means one lot of letters goes inside another.
'sport' becomes 'pont' (I am not sure about this - if you are sure you should believe this answer much more).
'an' becomes 'i' (Roman numeral for one).
'pont' going around 'i' is 'POINT'.
Can you help me to learn more?
(Other definitions for point that I've seen before include "... indicate location" , "Indicate with finger, may be sharp" , "Aim; sharp end" , "Importance < of level" , "Dot -- full stop" .)