On being caught in a tangled net, it's quite a weight (5)
I believe the answer is:
tonne
'weight' is the definition.
(I've seen this before)
'on being caught in a tangled net' is the wordplay.
'being caught in' means one lot of letters goes inside another.
'a tangled' is an anagram indicator.
'net' with letters rearranged gives 'tne'.
'on' going within 'tne' is 'TONNE'.
'it's quite a' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tonne that I've seen before include "A thousand kilogrammes" , "One thousand kilograms" , "1000 kilograms" , "Mass" , "Metric weight unit" .)