Ian and Pat involved in something that needs beating (6)
I believe the answer is:
pinata
'in something that needs beating' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'ian and pat involved' is the wordplay.
'and' says to put letters next to each other.
'involved' is an anagram indicator (involved can mean confusing or complex).
'ian' after 'pat' is 'patian'.
'patian' is an anagram of 'PINATA'.
Can you help me to learn more?
(Other definitions for pinata that I've seen before include "that's broken at party" , "Smashed party guest" , "Container suspended from a height for blindfolded children to break open with sticks" .)