Outsiders in league have penned type of clue for sport (8)
I believe the answer is:
lacrosse
'for sport' is the definition.
(lacrosse is a kind of sport)
'outsiders in league have penned type of' is the wordplay.
'outsiders in' says to hollow out the word (remove centre letters).
'have' indicates putting letters inside.
'penned type of' becomes 'across' (I can't justify this - if you can you should believe this answer much more).
'league' with its middle removed is 'le'.
'le' enclosing 'across' is 'LACROSSE'.
'clue' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for lacrosse that I've seen before include "Game played with nets on sticks" , "Game played with netted sticks" , "Like thirteen of the other clues in the French" , "Game played with a netted stick" , "Ball game using netted stick" .)