TENNIS is, in many ways, an old-fashioned sport. Most of the rules, from the layout of the playing surface to the scoring system, would be instantly recognizable to a player from a century ago. To the leaders of the game’s governing bodies, that isn’t necessarily a good thing. Matches are getting longer, the pace of play has slowed and fans are still expected to remain quiet during play, all of which threaten to slow the sport’s growth.

This November the Association of Tennis Professionals (ATP), the governing body of men’s tennis, will debut the NextGen ATP Finals, an exhibition showdown in Milan featuring the season’s eight best players aged 21 or younger. Last week the ATP announced that the event would serve as a proving ground for several innovations meant to modernise the sport and speed up play, including mid-match coaching, relaxed rules for spectators, an abbreviated warm-up, a shot clock, no-let serving and a new scoring system.

Many of these tweaks will have minor effects, at best. Although coaches are formally forbidden from providing guidance during a match, players still manage to communicate with their support teams as much as they can get away with. A shot clock might be a useful tool to shorten a Rafael Nadal match, but only a handful of players regularly exceed the current 25-second limit between points. And no-let serving—that is, requiring the returner to play serves that clip the top of the net and land in the service box—promises to trim no more than two minutes from the length of a typical match. Most jarring for players and fans will be the revised scoring system. Just as at the majors, competitors will still play to the best of five sets. However, the sets will be shorter: the first player to claim four games will win instead of the usual six; a tiebreak will be played at three-all; and within each game, a single winner-take-all point will replace the traditional “win by two” format at deuce. This last tweak, commonly dubbed “no-ad” scoring, is already used for ATP doubles, which has also replaced the third set with a first-to-ten-points “super tiebreak.” By eliminating the possibility of long games with endless deuces, the doubles format offers tournament organisers much more predictability for scheduling purposes: Only four doubles matches played under those rules this year have taken longer than two hours.

However, no-ad scoring comes at a cost. Long games feature passels of high-leverage points, the important moments that make for exciting tennis. The NextGen Finals format counter-balances the negative effect of no-ad by shortening sets: it prevents boring 6-0 or 6-1 blowouts. It also increases the probability that a set will end in a tiebreak, an alternative source of “high-leverage” points with a disproportionately large impact on the outcome of a match.

Like the doubles format, the NextGen Finals rules will both shorten the length of a typical match and cut down on schedule-busting marathons. A random sample of 50 recent ATP singles matches lasted an average of 144 points. When we simulated the same player matchups with the NextGen Finals rules, the mean duration fell to 114 points. At the margin, one point lasts around 40 seconds, so the new rules will trim about 20 minutes from the average match. The effect is even more dramatic on marathon matches: of the 50 matches, six required more than 200 points to complete. Yet in 5,000 simulations—100 of each contest—the 200-point mark was crossed only once.

How much excitement can we expect from these shorter matches? For that, we’ll need a metric called Excitement Index (EI), first devised for American football. It measures the importance of each play in terms of its potential impact on the final outcome, on the assumption that lots of high-leverage moments make for exciting sport. A boring patch, such as 40-love early in a set, cannot affect either player’s chances of winning more than 1% or so. In contrast, a single exciting point—like all those deuces the new format has sent to the chopping block—can promise a shift of 10% or more. EI averages all of those leverage measurements and multiplies by 1000, resulting in a range from about 10 (a one-sided blowout) to 100 (a memorable thriller).

On average, the NextGen Finals format will make matches a bit less exciting. It would reduce the overall EI of our 50-match sample from 51.4 to 46.7, and about 60% of the simulated replays were less exciting than the original match. However, the new rules certainly do not preclude the possibility of an exciting match entirely. The simulations reached EIs as high as 85, and most matches showed at least a one-in-ten chance of topping 60. In this regard, playing five shorter sets is a better option than employing the ATP doubles format. The no-ad, third-set super-tiebreak rules result in an average EI almost identical to that of the traditional format, but with far less variation: in exchange for reducing the number of dud matches, it also sharply lowers the probability of an unforgettable duel.

The atmosphere in Milan this November, with sets ending at four games, a prominent shot clock, and spectators milling about during play, would be almost unrecognisable to a tennis pro of a century ago. Yet compared to other alternative formats, it is positively staid. “Tiebreak Tens,” an exhibition held earlier this month in Madrid, featured eight elite professionals playing “matches” that consisted of a single first-to-ten tiebreak. The contests are very short and every point is crucial, but the results are so influenced by luck as to be nearly random. In contrast, the NextGen Finals rules provide for long enough matches that the better player is about as likely to win as he would be in a traditional best-of-three, all the while trimming match length at only a modest cost in excitement. Of all the alternative formats devised to make tennis more modern, this one is among the most promising.