Ran into a sailor, mariner missing bottom part of foot (10)
I believe the answer is:
metatarsal
'part of foot' is the definition.
('metatarsal' is part of 'foot')
'ran into a sailor mariner missing bottom' is the wordplay.
'ran into' becomes 'met'.
'sailor' becomes 'tar' (slang term for a sailor).
'mariner missing bottom' becomes 'sal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'met'+'a'+'tar'+'sal'='METATARSAL'
Can you help me to learn more?
(Other definitions for metatarsal that I've seen before include "Bone in the foot" , "Part of foot" .)