Grand Slam tournaments are planning to return to seeding only 16 players, instead of 32, as of 2019, and now will give a player who is a late withdrawal because of an injury 50 percent of the first-round prize money.

Also among the announcements by the Grand Slam Board on Tuesday after two days of meetings in London last week:

— A player who retires from a first-round match or "performs below professional standards" could face a fine as high as the entire prize money due a loser in that round.

— A 25-second serve clock will be tried out at the Australian Open in January, but like at this year's U.S. Open, not during main-draw matches.

— Players could be fined up to $20,000 for violating "strictly enforced" prematch timing, which will give them one minute to meet at the net after walking on the court, five minutes for warming up, followed by one minute to be ready for play to begin.

The four Grand Slam tournaments — the Australian Open, French Open, Wimbledon, U.S. Open — doubled the number of seeded players to 32 in June 2001. That decision was made partly in response to complaints from clay-court specialists that they wanted more draw protection at Wimbledon, the only major tournament played on grass.

Going back to 16 seeds in 2019 would, in theory anyway, make early upsets more likely. That's because if all of the highest-ranked players enter the field, whoever is No. 1 could wind up facing whoever is No. 17 in the opening round.

With 32 seeds, none was forced to play someone ranked higher than No. 33 before the third round.

The changes with regard to first-round withdrawals, retirements and lack of full effort appear to be in response to what happened at Wimbledon this year. Novak Djokovic's first-round match at Centre Court lasted all of 40 minutes, and Roger Federer's went 43, before their opponents stopped playing because of pre-existing injuries. Two other men also stopped mid-match that day, bringing the first-round retirement total to seven and sparking discussion about whether spectators were being shortchanged.

The rule changes issued Tuesday, and taking effect next year, let players collect half of the first-round prize money at a Grand Slam tournament if they are "unfit to play" and withdraw onsite after noon on Thursday but before the main draw begins. The person replacing them in the field — a "lucky loser" who failed to advance out of the qualifying rounds — will get the other half of that money, plus whatever they might accumulate by winning matches.

The reasoning: Injured or ill players won't start a match simply to collect their prize money before quitting.

The 25-second serve clock gives players 5 more seconds than ATP rules currently allow on the men's tour. But Grand Slam Board Director Bill Babcock said the clock will be used at the 2018 Australian Open on a trial basis the way it was at the U.S. Open, which tested it only for events such as qualifying and junior matches.

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