Teacher pinching student's rear creates excitement (4)
I believe the answer is:
stir
'excitement' is the definition.
('stir' can be a synonym of 'excitement')
'teacher pinching student's rear' is the wordplay.
'teacher' becomes 'sir' (I've seen this before**).
'pinching' means one lot of letters goes inside another (taking inside).
'rear' suggests the final letters (the back of the word).
The last letter of 'student' is 't'.
'sir' going around 't' is 'STIR'.
'creates' is the link.
(Other definitions for stir that I've seen before include "Bustle, activity" , "Create revolutionary movement" , "Stimulate; prison" , "in which you'll find people with convictions" , "Uproar" .)