Rare event in field that may involve a couple of ducks (3,5)

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

When a bowler gets a hat trick in cricket, at least two of the batters will have scored a duck. Thanks to several commenters who point out that this is not necessarily the case. The clue says “may involve” so Vulcan gets a pass, even if I don’t.