Jordan Spieth was one shot back of the lead on No. 8 tee in the final round of the 2015 British Open on the Old Course at St. Andrews, and he knocked his tee shot at the 174-yard par 3 onto the green. Normally that would be cause for at least a little satisfaction, but not necessarily on the Old Course.

That’s because most of the putting surfaces on the Old Course – which this week hosts its 30th British Open – are gigantic double greens that serve two holes with flagsticks planted on opposite sides. As can so easily happen after an approach shot finds the wrong portion of one of these greens, Spieth faced a putt of some 100 feet. His ensuing four-putt – his first attempt sailed off the green ­– and the double-bogey 5 left him playing catchup the rest of the day, and he eventually fell one shot short of a playoff won by Zach Johnson.

Yardage book: The Old Course at St. Andrews  Golfweek’s Best ranking of the rota of host courses The 10 best golf courses in Scotland British Open tee times, TV and streaming info

None of this is a knock on Spieth’s putting – he was a top-10 putter on the PGA Tour that year, and that double bogey clearly was caused by an errant iron shot. On a normal course, Spieth would have missed the green, likely by a wide margin, and he probably would have pitched a wedge shot of some kind onto the putting surface without ever leaving such a dent in his putting stats.

The Old Course is different, and errant iron shots don’t always lead to pitches or chips. Instead, players often face massive putts for which they must judge distance, extreme mounding and even the wind if they are to have any hope of getting their first putt close.

The Old Course has only four greens that serve just one hole, at Nos. 1, 9, 17 and 18. The rest of the holes play to one side of seven giant double greens. An interesting note for the hardcore golf nerds: If the two hole numbers served by a double green are added together, they always equal 18. For example, No. 2 and No. 16 share a green, so they equal 18. Other shared greens are Nos. 3 and 15, Nos. 4 and 14, Nos. 5 and 13, Nos. 6 and 12, Nos. 7 and 11, and Nos. 8 and 10.

And they are huge.

The average size of the putting surfaces at the Old Course is 22,267 square feet, more than half an acre, and the double green for Nos. 5 and 13 is over 37,000 square feet. By comparison, the average green size at Pebble Beach Golf Links, another seaside course famed for hosting major championships, is about 3,500 feet. Augusta National, another major staple, has greens that average just over 6,400 square feet.

Even if you halve the size of the double greens at the Old Course to make an apples-to-apples comparison equaling 18 greens, the putting surfaces at the Old average more than 13,600 feet per hole, nearly four times the size of the greens at Pebble Beach.

Perhaps most telling, several of the double greens are more than 100 yards across. Play to the wrong flag – it happens, even for the pros – and you will face one of the longest putts of your life.

The out-and-back layout of the Old Course makes such greens possible, as most of the holes are situated in a long, somewhat narrow stretch of land between other courses as they play away from the massive R&A clubhouse toward an estuary before turning back toward the clubhouse. Parallel holes play in opposite directions through the corridor, making it possible to approach the shared double greens from opposite directions.

And their size isn’t their only feature. The greens of the Old Course are packed with humps and hollows that following the natural contours of the lumpy ground. Some of the slopes wouldn’t work on smaller putting surfaces, but because the greens of the Old Course are so big, the extreme contours fit. If a modern designer tried to squeeze such slopes into a normal-sized green, there would be almost no puttable areas were a ball would stop rolling, and the usable portion of the green would be too small.

The size, the slopes – they all factors into strategy and thinking. The Old Course requires precision, often along the ground, to small targets within giant greens. Even with big overall targets, big misses still lead to big numbers.

Two of the best American public-access examples of such huge greens would be Old Macdonald at Bandon Dunes Golf Resort in Oregon and Streamsong’s Black Course in Florida, both of them modern courses where three-putts, four-putts and worse happen every day. Like the Old Course, the greens at Old Mac and the Black feature tremendous contours that force players to concentrate on hitting small targets within all that square-footage.

The perfect example as we head into this week’s British Open was Spieth’s four-putt in 2015, when he proved that a green hit in regulation doesn’t always mean much at St. Andrews.