Hit with bars -- the cause of being in stitches? (10)

I believe the answer is:

punchlines

'the cause of being in stitches?' is the definition.
(funny punchlines might have you in stitches)

'hit with bars' is the wordplay.
'hit' becomes 'punch' (punching is a kind of hitting).
'with' is a charade indicator (letters next to each other).
'bars' becomes 'lines' (bar can mean a line).
'punch'+'lines'='PUNCHLINES'

I've seen this clue in The Telegraph.

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