Eggs upset deer (7)
I believe the answer is:
roebuck
'deer' is the definition.
(roebuck is a kind of deer)
'eggs upset' is the wordplay.
'eggs' becomes 'roe' (I've seen this before).
'upset' becomes 'buck' (I can't explain this - if you can you should believe this answer much more).
'roe'+'buck'='ROEBUCK'
Can you help me to learn more?
(Other definitions for roebuck that I've seen before include "Graceful creature" , "Providing venison" , "Type of male deer" , "reddish-brown jumper" , "Small male deer" .)