Overdo funny extra gag in middle of speech (10)
I believe the answer is:
exaggerate
'overdo' is the definition.
(I know that overdo can be written as exaggerate)
'funny extra gag in middle of speech' is the wordplay.
'funny' is an anagram indicator.
'in' is an insertion indicator.
'middle of' means to look at the middle letters.
The centre of 'speech' is 'ee'.
'extra'+'gag'='extragag'
'extragag' with letters rearranged gives 'xaggerat'.
'xaggerat' inserted inside 'ee' is 'EXAGGERATE'.
(Other definitions for exaggerate that I've seen before include "Stretch" , "Overdo" , "Overstate; intensify" , "Overstate unduly" .)