One at the head of averages? (6)
I believe the answer is:
Here is my best explanation:
'head of averages?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I can't explain the rest of the clue.
(Other definitions for bowler that I've seen before include "Cricket thrower or posh hat", "Cricketer and round hat", "Hard hat for cricket thrower", "Posh hat or cricket player", "Hat (for cricketer?)", "Type of hat", "One who can deliver", "Caddick; hat", "Cricket player or hard hat" and "Sportsman".)