Sports venue in Delaware, namely (5)
I believe the answer is:
arena
'sports venue' is the definition.
(I've seen this before)
'in delaware namely' is the wordplay.
'in' says the answer is hidden in the clue.
'ARENA' can be found hidden inside 'delaware namely'.
(Other definitions for arena that I've seen before include "Action space in centre of amphitheatre" , "Sphere of intense activity" , "Venue for contests" , "Venue for boxing, circus and other action events" , "Entertainments venue" .)