There’s a reason enlightened players carry a marker pen in their golf bag. Identifying that the ball you’re about to play is actually yours is like Golf 101, right? Surprisingly, playing the wrong ball happens a lot more frequently than you might expect. And it’s not just rank-and-file golfers that violate this rule.

There have been a number of incidents on the pro tours in recent years where golfers have played the wrong ball with disastrous — and expensive — consequences. Mark Hensby was assessed a 10-stroke penalty, yep 10 strokes, for playing a wrong ball in the 2021 Palmetto Championship.

In 2022, Mackenzie Hughes got hosed at the Farmers Insurance Open when a volunteer set a flag down next to a ball in the rough that turned out to be another player’s ball. He played it, took a triple after the penalty, and ended up missing the cut.

We could go on, but you get the idea. You’re not alone if you’ve mistakenly played someone else’s ball. (We’ll get into incidents when a golfer intentionally plays someone else’s ball a little later in this article. That happens, too).

So how do you proceed if you accidentally play a wrong ball? Under Rule 6.3c, in match play you lose the hole. In stroke play, it’s a two-shot penalty and you must correct the mistake by going back and playing your ball to finish the hole. If your ball is lost, proceed under the stroke-and-distance penalty (yes, that means a third extra stroke to your score, sorry!)

This rule is pretty easy to understand, but let’s take a slightly deeper look at a few wrong-ball scenarios that often happen. One is when opponents in match play happen to hit each other’s golf balls. The way to handle this situation is to assess the loss-of-hole penalty to the player who hit the wrong ball first. If you and your opponent aren’t sure who hit first, there is no penalty and you should play out the hole with each other’s golf balls.

And to clarify the stroke-play procedure, you’re only hit with two shots for playing a wrong ball no matter how many strokes you take on a given hole with it. However, if you start the next hole with the wrong ball, you’re disqualified. If you’re wondering why Hensby wasn’t DQd, it’s because the tournament was using Model Local Rule G-4 allowing for a two-shot penalty on each hole where the player used a wrong ball.

Oh, and if you’re wondering what happens to a golfer who intentionally plays a wrong ball and is caught, well, Rule 1.2 covers it. The cheat is banished.