Trespass for one snaring new bird without tail (8)
I believe the answer is:
encroach
'trespass' is the definition.
(I know that encroach is a type of trespass)
'for one snaring new bird without tail' is the wordplay.
'for one' becomes 'each' (eg something may be one pound each or for one).
'snaring' means one lot of letters goes inside another.
'new' becomes 'ncr' (I can't explain this - if you can you should give a lot more credence to this answer).
'bird' becomes 'oo'.
'without tail' means to remove the last letter.
'oo' with its final letter taken off is 'o'.
'ncr'+'o'='ncro'
'each' enclosing 'ncro' is 'ENCROACH'.
(Other definitions for encroach that I've seen before include "Enter upon another's property or rights" , "Go past a normal limit" , "Gradually intrude (upon another's space)" , "Intrude on someone's territory or time" , "Advance beyond the usual limit" .)