Evidence given by grass auditors introduced
I believe the answer is:
hearsay
'evidence' is the definition.
(hearsay evidence is a kind of evidence)
'grass auditors introduced' is the wordplay.
'grass' becomes 'hay' (I have seen 'Mown grass ' mean 'hay' so perhaps 'grass' could also mean 'hay').
'auditors' becomes 'ears' (I've seen this before).
'introduced' means one lot of letters goes inside another.
'hay' going around 'ears' is 'HEARSAY'.
'given by' acts as a link.
(Other definitions for hearsay that I've seen before include "Testimony not based on direct knowledge" , "Gossip or idle talk - it's not evidence" , "speculation" , "Based on report given by others" , "Kind of rumour, makes bad evidence" .)