Runs in pursuit of beam (6)
I believe the answer is:
rafter
'beam' is the definition.
(I know that rafter is a type of beam)
'runs in pursuit' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'in pursuit' becomes 'after' (I've seen this in another clue).
'r'+'after'='RAFTER'
'of' acts as a link.
(Other definitions for rafter that I've seen before include "support" , "Sloping roof timber" , "person on floating logs" , "Sloping beam that supports the roof" , "Roofing beam" .)