Can't foul in the box, one might be feeling (8)
I believe the answer is:
tentacle
'one might be feeling' is the definition.
(animal limb used for feeling or touching)
'can't foul in the box' is the wordplay.
'foul' is an anagram indicator.
'in' is an insertion indicator.
'the box' becomes 'tele' (both can informally mean television).
'cant' is an anagram of 'ntac'.
'ntac' placed inside 'tele' is 'TENTACLE'.
(Other definitions for tentacle that I've seen before include "One may be feeling" , "Organ used for grasping and feeding" , "one feels" , "Octopus feeler" , "Octopus's "arm"" .)