Welshman wrapping one leg around head of travelling preacher (10)
I believe the answer is:
evangelist
'preacher' is the definition.
(evangelist is a kind of preacher)
'welshman wrapping one leg around head of travelling' is the wordplay.
'welshman' becomes 'evans' (common Welsh surname).
'wrapping' means one lot of letters goes inside another.
'one leg around' becomes 'geli' (I am not sure about this - if you are sure you should believe this answer much more).
'head of' indicates taking the first letters.
The first letter of 'travelling' is 't'.
'evans' enclosing 'geli' is 'evangelis'.
'evangelis'+'t'='EVANGELIST'
(Other definitions for evangelist that I've seen before include "Mark for one" , "Zealous advocate" , "Gospel spreader" , "Gospel writer" , "Preacher" .)