Old union leader, teased and got the better of (9)
I believe the answer is:
outwitted
'got the better of' is the definition.
(I've seen this before)
'old union leader teased' is the wordplay.
'leader' says to take the initial letters.
'teased' becomes 'twitted' ('twit' can be a synonym of 'tease').
The initial letters of 'old union' is 'ou'.
'ou'+'twitted'='OUTWITTED'
'and' acts as a link.
(Other definitions for outwitted that I've seen before include "beaten" , "Was too clever for" , "surpassed in ingenuity" , "fooled" , "Deceived by greater ingenuity" .)