When the weather threatens to rain out a baseball game, the groundskeepers cover the infield with a tarp to protect it from damage.

Generally, Major League Baseball teams will continue play in light to moderate rain but will suspend play if it is raining heavily or if there is standing water on the field. Games can also be delayed or canceled for other forms of inclement weather, or if the field is found to be unfit for play, and for other unusual causes such as bees. Bee delays and cancellations have occurred in games such as the spring training game in 2005 that was canceled, as well as the 2009 Astros-Padres game that was delayed in the ninth inning. However, rain is by far the most common cause for cancellations or stoppages of play.

Before a baseball game commences, unless it is the second game of a doubleheader, the manager of the home team is in charge of deciding whether or not the game should be delayed or canceled due to rain or other inclement weather (see Rule 3.10 of baseball’s Official Rules). Once the home team manager hands his lineup card to the umpire shortly before the game is to begin, the umpire-in-chief has sole discretion to decide if a game should be delayed or canceled (see Rule 3.10 and Rule 4.01 of the Official Rules). This also applies to the second game of a doubleheader. Umpires are required by rule to wait at least 30 minutes to see if conditions improve; this is referred to as a rain delay and is not counted as part of the length of the game listed in the box score. In practice, umpires are encouraged to see that games are played if at all possible, and will sometimes wait as long as three hours before declaring a rainout.

If a game is rained out before play begins, it is rescheduled for a later date. If it has already begun and rain falls, several scenarios are used to determine the need to resume play:

• If the game has completed the top half of the 5th inning and the home team is ahead, the game can be deemed an official game. The home team is declared the winner, and the game officially counts in standings.
• If the game has completed the bottom half of the 5th inning and either team is ahead, the game can be deemed an official game. The leading team is declared the winner, and the game officially counts in standings. In some Minor League Baseball and college games, this scenario is possible only in the final day of a series.
• If the game has completed the 5th inning, and the teams are tied, if the game is a playoff game (regardless of inning), or in college and some Minor League Baseball games, it is not the final game in the series (the first or second game in a three-game series, also regardless of inning), the game is considered suspended, and the resumption of the game is scheduled for a future date (usually the following day). The game picks up from where it left off.
• If none of the previous three scenarios apply, the game can not be deemed official. The umpire declares "No Game," and a make-up of the game is scheduled for a future date unless it is not feasible (most likely end of season, half in some minor leagues, or in college). The statistics compiled during the rained out game are not counted.
  
  Motorsport

Some auto racing series do not compete in rain, especially series that race on paved oval tracks. The rain severely diminishes the traction between the slick tires and the racing surface. Other series, especially those that race on road courses such as Formula One, use special treaded rain tires while the racing surface is wet but not in heavy rain. Dirt track racing can be run in a light rain as the vehicles have treaded tires. Rallying can be held in rain or snow.

The NASCAR Sprint Cup Series and the IRL IndyCar Series do not compete on a wet or moist surface at most oval tracks. They will not start an event unless the surface is dry. If the surface become wet during a race, the event is typically halted, and the cars are pulled off the track. Very light moisture may warrant only a temporary yellow caution period, while heavier rains usually require a red flag, stopped condition.

After the rain ceases, the sanctioning body will determine if the track surface can be dried within a reasonable time frame. The track is considered "lost" if rain thoroughly wets the surface, usually characterized by a dark look to the asphalt or concrete pavement. Track crews use jet dryers, which consist of modified jet engines, mounted upside down to allow the hot exhaust to pummel the surface. The hot exhaust acts to quickly evaporate the rainwater, and allow the surface to dry considerably quicker than normal conditions. Large scale wet-vacs are also sometimes used to supplement.

If rain does not subside, the sanctioning body has several options. Typically, the race is considered "official" if at least half of the advertised distance (similar to baseball) has been completed. If such is the case, the race is deemed complete, and the winner can be declared. In some cases, if the race has already gone beyond the halfway point (especially if it is very near the scheduled finish) when rain falls, and the weather forecast is for day-long rain, no attempt to complete the remainder of the race will be attempted. If a downpour occurs very near the end of the race, the officials, in fact, may use their authority to wave the checkered flag at that instant, and end the race immediately. (This occurred during the 1975 Indianapolis 500).

The IndyCar Series and Nationwide Series will use rain tires if they are at a road course. The Sprint Cup Series has experimented with rain tires, but does not currently use them. However, if the rain is severe enough, the race will be stopped.

The code in USAC, NASCAR, and IRL states if fewer than half the laps are completed or if the race is unable to start, the event is resumed on a later date, usually the next day. With the introduction of lights at numerous oval tracks, the time frame for resuming a rain delayed race on the same day has been largely expanded. Some races stopped during the day for rain have seen the track dried, and the race completed later in the evening on the same day.

Most road racing (except in the United States) do not use the 50 percent rule. In Formula One, if severe rain forces the race to be interrupted, the regulations state if less than three laps were completed, the race is cancelled and will not be made up. Once a race is on its fourth lap, the race is official, and only half points will be awarded until 75% of the race has been completed.

The 2009 Petit Le Mans in Braselton, Georgia, was an example of a rainout where less than half the race (184 of 394 laps). The red flag waved after 184 laps at the 4:52 point of the race. In endurance racing, the clock does not stop for red flags. IMSA waited until 8 PM to declare the race official. While the race was 13 laps from official (500 miles), the clock had passed the five hour mark when the race was called at 8 PM.

Other sports

Other sports typically stopped due to the onset of rain include golf, tennis, and cricket, where damp conditions seriously affect playing quality and the players’ safety. In the case of tennis, several venues (such as those of Wimbledon and the Australian Open) have built retractable roofs atop of their existing courts and stadiums in the last decade to avert rain delays that could push a tournament further than the final date.

Association football generally plays on through rain, although matches can be abandoned if the pitch becomes severely waterlogged or there is lightning in the area, with the latter case being more for the protection of spectators within the metal stands surrounding stadiums. In NCAA play, should lightning be detected by any pitch official, a minimum 30-minute delay and a potential "rainout" can be declared if the lightning continues for a considerable amount of time under the NCAA’s all-sports policy regarding lightning. If there is severe rain during a match, it can become a point of controversy whether a match should be abandoned. A notable example of this was on the final day of the Serie A 1999-00 season, when Juventus had to play out a match against Perugia despite the pitch appearing to be unplayable. Juventus lost the match 1-0 and consequently lost the Scudetto to Lazio.