Unruly trade unionists took off Rossini and teased him (7)

I believe the answer is:

taunted

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'teased him' is the definition.
'taunted' can be an answer for 'teased' ('taunt' can be a synonym of 'tease'). I am unsure of the 'him' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for taunted that I've seen before include "Mocked, jeered" , "Deliberately provoked by poking fun at" , "Jeered at in a cruel and hurtful way" , "Derided, mocked" , "Twitted" .)

I've seen this clue in The Irish Times.

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