... in which run of learner drivers may end in a tumble (4)
I believe the answer is:
roll
'a tumble' is the definition.
(thesaurus)
'in which run of learner drivers may end' is the wordplay.
I cannot really understand how this works, but
'run' could be 'r' (cricket abbreviation) and 'r' is present in the answer.
'of' could be 'o' and 'o' is present in the answer.
'learner' could be 'l' and 'l' is located in the answer.
A single letter 'l' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for roll that I've seen before include "Move like a ball" , "Small round piece of bread" , "directory" , "At school it may be called" , "on which one is regularly successful" .)