The son went off and lumbered one with (7)
I believe the answer is:
saddled
'the son went' is the definition.
I can't tell whether this defines the answer.
'off and lumbered one with' is the wordplay.
'off' becomes 'addled' (I've seen this before).
'and' says to put letters next to each other.
'lumbered one with' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'addled' put after 's' is 'SADDLED'.
Can you help me to learn more?
(Other definitions for saddled that I've seen before include "stuck" , "Horse might be" , "Encumbered" , "Burdened with" , "Having to put up (with) - ready to be ridden" .)