Theresa grabbing Romeo's hair (5)
I believe the answer is:
tress
'hair' is the definition.
(I know that tress is a type of hairdo)
'theresa grabbing romeo's' is the wordplay.
'theresa' becomes 'tess'.
'grabbing' means one lot of letters goes inside another.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'tess' placed around 'r' is 'TRESS'.
(Other definitions for tress that I've seen before include "Switch" , "is a bit of a shock" , "Obsolete support" , "Rests (anag.)" , "Long piece of hair" .)