Follow on with witness covering sawn-off gun (5)
I believe the answer is:
segue
'follow on' is the definition.
(I've seen this before)
'witness covering sawn-off gun' is the wordplay.
'witness' becomes 'see' (synonyms).
'covering' means one lot of letters goes inside another.
'sawn-off' means to remove the last letter.
'gun' with its final letter taken off is 'gu'.
'see' enclosing 'gu' is 'SEGUE'.
'with' is the link.
(Other definitions for segue that I've seen before include "Smooth musical transition" , "Move smoothly from one musical piece to another" , "Keep going without interruption" , "carry on" , "Move continuously from one song to another" .)