Upset, tease and study groups of politicians with numerous outdoor events (6,7)
I believe the answer is:
garden parties
'numerous outdoor events' is the definition.
Although both the answer and definition are plural nouns, I can't see how one could define the other.
'upset tease and study groups of politicians' is the wordplay.
'upset' is a reversal indicator.
'tease' becomes 'rag' ('rag' can be a synonym of 'tease').
'and' says to put letters next to each other.
'study' becomes 'den' (I've seen this before).
'groups of politicians' becomes 'parties' (I can't explain this - if you can you should believe this answer much more).
'rag' written backwards gives 'gar'.
'gar'+'den'+'parties'='GARDEN PARTIES'
'with' acts as a link.
Can you help me to learn more?
(Another definition for garden parties that I've seen is " Fun in summer".)