You're standing over a putt, and you think you've got the line. The breeze is blowing, but you don't care. This thing is going in. You stroke the putt, and the ball is on its way to the hole when...BAM! a leaf comes through, hits your ball and knocks it offline.
Naturally, you're in shock. This kind of thing is uncommon in golf. But what do you do from there? Do you simply take your lumps and hole out the next putt? Actually, under the Rules of Golf, you're not only allowed a re-do, but you're required to re-do the putt.
As Matthew Southgate found out the hard way in the Web.com Tour Finals, the Rules of Golf under Rule 19-1 make it clear: If what's called "outside agency" (leaf, shoe, fellow competitor, opponent's caddie, equipment, etc., but not a bug or a worm or wind) stops or deflects a ball after a putting stroke has been made, then that stroke doesn't count. In fact, the remedy is for a player to replace their ball back to the spot where they struck the putt and re-do it. And if a player doesn't cancel the stroke and replay it from the original position, the penalty in stroke play is actually 2 strokes.
So, the good news is that if something other than an insect or worm stops your ball while it's rolling, you get a second chance. The bad news is that if you don't know that's the rule, then you can pay a huge price.