Dog runs off at first call from umpire (4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[r] OVER (supposedly a common name for a dog) with the initial R (abbreviation for runs, in cricket scoring) removed (runs off at first). In cricket, the umpire calls “over” after a sequence of six legally-bowled balls, to indicate that the next bowler should start from the opposite end.