The ultimate contradiction in tennis is the unforced error.

This statistic suggests players should not commit errors, but tennis is a game of errors much more than winners.

Entering the singles semifinals at the French Open this year, 67 percent of the men’s points and 69 percent of the women’s points ended in errors.

But next to nothing happens in a match without some form of pressure. A player marginally leans to the left in the middle of a point, and the opponent catches it in his or her peripheral vision and changes a shot at the last second seeking a strategic advantage. That is labeled an unforced error. It’s not. There is always something forcing or influencing shot selection.

Or say a player struggles with slow, high balls in the middle of the court. They look easy, but they are missed a lot because players make contact high, out of their strike zone, and there is no power to work with. Is that an unforced error, or just smart strategy by the opponent?

Unforced errors are not even the No. 1 error that occurs in a match, yet they have pushed the more abundant forced error statistic into oblivion.

In the men’s draw at Roland Garros for the past two years, forced errors have outnumbered unforced errors, 17,738 points to 17,056 points, but you would never know it. Forced errors are not a line item on the tournament statistics page.

Forced errors are left off because they are seen as ambiguous or unimportant. You have to add winners and unforced errors, and subtract that number from total points to figure out a player’s forced error total.

Forced errors are what players should obsess over. Get control of the point, and make the opponent miss. It’s repeatable, and forms the beating heart of game plans.

Errors in a tennis match are matters of opinion. A part-time statistician or student sits on the side of the court and evaluates the game style, execution, technique and tactical battle between professional players and decides what’s forced and what’s unforced.

The eight ways to force an error in tennis are: consistency, direction, depth, height, spin, power, court position and time (taking time away for the opponent to prepare for a shot).

The history of the unforced error can be traced to 1982, when Leo Levin, who played at Foothill College in Los Altos Hills, Calif., decided to chart his teammates’ matches. He tracked the errors they were making and the errors their opponents were forcing them to make.

“That concept of forced and unforced errors kind of came into being around that time, and then I got hired on by a company that was starting to develop the first computerized stats system,” Levin said in a recent interview at Roland Garros.

He is now the director of sports analytics for SMT, which collects data at all four Grand Slam tournaments.

“We came up with a concept saying that every point ended in one of three ways,” Levin said. “A winner, a forced error or an unforced error, and every single stroke, every single result, fit into one of those categories.”

The theory was solid, but something got lost along the way. Winners are objective; errors could be too.

Now, the unforced error is a judgement call, with a healthy gray area.

On the opening point of his first service game against Rafael Nadal on Monday in the French Open, Maximilian Marterer got into an eight-shot rally and committed a forehand error to lose the point. It was labeled an unforced error.