Since the 2019 change to RULE 13.2a(2), this answer continues to come down to personal preference, but there is actual data on the matter put forth by actual experts.
The definitive article on pulling the flagstick was published by Golf Digest and updated October 11, 2023. It focuses on the research of Tom Mase, a professor of mechanical engineering at Cal Poly with stints at both Callaway and Titleist, as well as an original member of the Golf Digest Hot List Technical Advisory Panel. For all practical purposes, he’s a golf scientist. His experiment ran six separate sessions with the Cal Poly golf team at their practice facility, Dairy Creek Golf Course.
While the article’s headline, “The science behind why the flagstick should be pulled 99.9 percent of the time,” has a clickbait ring to it, the statement is 100% correct if, and this is a big if, you play on the PGA Tour. The exercise uses PGA Tour statistics for accuracy and frequency of putts made from certain distances. So regardless of hitting the flagstick straight on or off-center, the length of putt, speed of green, or type of flagstick (more on this later), the case is closed and the pin should come out if you’re a professional golfer.
The only time the flagstick “helped” a putt was when the ball travelled at a high velocity, enough to run 9 feet or more past the hole. (“Nice putt, Arnold.) So here’s the thing, when was the last time Jason Day ran a putt 9 feet past the hole? With the exception of maybe an Augusta green, it isn’t something you see very often from any pro.
Just like the pros, it still makes sense for the rest of us to pull the pin for most situations. The exception being any putt where there is a chance the ball is traveling fast enough to run 9 feet past the hole. Taking away false fronts, moguls, and undulations, and this could be the case for lag putts, longer downhill putts, putts from the fringe or off the green, and very fast greens. How far away does 9 feet come into play? Well, it depends on the golfer. Certainly the higher the handicap the closer that point is, but 30 feet out sounds like a good threshold where we start to ask ourselves the question of whether to leave the pin in. Even though it’s a quite arbitrary number, there’s no need to think about this decision with putts of 30 feet or less. Over 30 feet and most amateur golfers can decide for themselves based on green speed, putting competency, confidence in the read, and situation. Exceptions and adjustments to the 30-foot mark should be made if the putt is downhill, especially if significantly so.
For situations where it makes sense to leave the pin in, there’s an entirely different experiment to reference and knowing the width of the flagstick becomes important. Rich Gagnon, Superintendent at Segregansett Country Club tested three different flagsticks manufactured by Par Aide to see how each reacts when struck by a golf ball. It is important to note that while the test involved balls rolling on the green at the hole from a PVC pipe, he was testing the flagsticks for holing a chip from off the green versus putting.
The flagstick test group:
In the experiment, the half-inch flagstick won out with 5% more balls in the cup than the three-quarter inch flagstick. Not a ton of difference so you don’t need a ruler with you to determine half and inch versus three-quarters, but with the one-inch flagstick, no balls dropped in the hole despite the fact that the bottom 12 inches of all three flagsticks are exactly the same width (1.5 inches) and made of fiberglass. You might need to read that again but the big takeaway from Mr. Gagnon’s experiment is to never leave a one-inch flagstick in the hole.
All of this being said and research aside, there’s one other reason to pull the pin – Is there a better sound than when your ball hits the bottom of the cup?
TL;DR: If you’re a professional golfer, pull the pin. If you’re an average golfer, pull the pin on any putt you could miss by more than 9 feet. Never, ever leave a one-inch flagstick in the hole.