Peter goes after a bit of fun, but it's risky (6)
I believe the answer is:
unsafe
'it's risky' is the definition.
(similar in meaning)
'peter goes after a bit of fun' is the wordplay.
'peter' becomes 'safe' (slang term).
'goes after' says to put letters next to each other.
'a bit of fun' becomes 'un' (I can't justify this - if you can you should give a lot more credence to this answer).
'safe' put after 'un' is 'UNSAFE'.
'but' is the link.
Can you help me to learn more?
(Other definitions for unsafe that I've seen before include "Hazardous" , "Dangerous, insecure" , "Dangerous - legally without basis" , "Risky - inadequately evidenced" , "giving no protection" .)