Applause about a first triumph but you really can’t trust them (8)
I believe the answer is:
cheaters
'you really can't trust them' is the definition.
I can't judge whether this defines the answer.
'applause about a first triumph but' is the wordplay.
'applause' becomes 'cheer'.
'about' is an insertion indicator.
'first triumph' becomes 't' (sst letter of 'triumph').
'but' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'t'='at'
'cheer' going around 'at' is 'cheater'.
'cheater'+'s'='CHEATERS'
Can you help me to learn more?
(Other definitions for cheaters that I've seen before include "who flout the rules" , "Teachers for swindlers" , "Deceivers, swindlers" .)