Japanese High School Baseball Championship

The National High School Baseball Championship (全国高等学校野球選手権大会, Zenkoku Kōtō Gakkō Yakyū Senshuken Taikai) of Japan, commonly known as "Summer Koshien" (夏の甲子園, Natsu no Kōshien), is an annual nationwide high school baseball tournament. It is the largest scale amateur sport event in Japan.

The tournament, organized by the Japan High School Baseball Federation and Asahi Shimbun, takes place during the summer school vacation period, culminating in a two-week final tournament stage with 49 teams in August at Hanshin Koshien Stadium (阪神甲子園球場, Hanshin Kōshien Kyūjō) in the Koshien district of Nishinomiya City, Hyōgo, Japan.

In the past teams from overseas have participated in the tournament. Korea fielded teams from 1921 to 1940; both Taiwan and Manchuria had teams participate from 1923 to 1940.

The 49 schools taking part in the final tourney represent regional champions of each of the prefectures of Japan (with two from Hokkaidō and Tokyo). From mid-June until July, regional tournaments are held to decide who is sent to Koshien.

The rules are the same as in the National High School Baseball Invitational Tournament. It is a single elimination tournament with nine inning games. Until 2021, games were declared official after seven complete innings in the case of suspension (due to weather, et cetera), except for the championship game which must be played to completion. Starting in 2022, games must last nine innings unless the run rule is in effect. If a game is suspended for inclement weather, the game will resume at point of interruption and will play the full length of game. For the regional tournaments, games are ended if one team leads by at least ten runs after five innings or seven runs after seven innings, except in the championship games. Designated hitters are not used. Four umpires are used, except for night games in which two outfield line umpires are added.

The first round pairings and byes are decided by lottery. 34 teams meet in the first round, and 15 teams with byes join at the second round (32 teams play in the second round). Therefore, it takes either five or six wins for a team to win the championship. Until 2002, the four quarter finals were played in one day, but this was changed to two a day over two days to give the players time off. If rain outs continue for more than three days, four games are played in one day. This occurred in 2003, so the first time the quarter finals were played over two days was actually 2004. To accommodate the extra day, the long tradition of starting the tournament on August 8 was changed to start a day or two early.

Up to four games are played each day until the quarter finals. The starting times of each day's games is shown below. Following games are begun about 30 minutes after the previous game ends. Due to the fast pace of the pitching, four games in one day are usually completed before sunset.

For tournaments previous to 1958 there were no extra inning limits for a game tied after nine innings of play. In 1933, Masao Yoshida had pitched a complete game during a 25 inning shutout in the semifinal, an all-time record. Yoshida had thrown 336 pitches during that game.