Did he run riot in Dunfermline? (5)

I believe the answer is:

miler

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But I can't explain it at all! Could you help me understand?

(Other definitions for miler that I've seen before include "one who competes in the long run" , "horse" , "Pre-metric middle-distance runner" , "Athlete running 1,760 yards" , "Runner over a specific distance" .)

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