A 900 series refers to three consecutive perfect games bowled by an individual bowler. A 300 is a perfect score in one game, thus a player's score would be 900 in a series of three consecutive games (the typical number of games in a single league session). To achieve the feat, a bowler would have to bowl 36 consecutive strikes. To date, 29 individuals have bowled a total of 30 certified 900 series (that is, 900s that have been officially recognized by the United States Bowling Congress, the sport's national governing body in the United States).
900 series (bowling) Wikipedia
On 1 July 1982, Glenn Allison bowled the first 900 series to be recorded in sanctioned league play, although it was not officially certified by the American Bowling Congress due to "non-compliant" lane conditions. To this day, there is a "cult following" supporting Glenn Allison and urging the USBC to officially recognize him as the first bowler to achieve a perfect series, especially because it was accomplished before the era of reactive bowling balls, and other scores in the bowling center that night were not unusually high. However, the USBC still refuses to sanction Allison's 900 series after concluding a re-evaluation in 2014, stating among other things that it would call into question all other honor score applications from that era.
In fact, the first six 900 series reported in ABC league play were all rejected for certification. The first perfect series to be officially sanctioned by the ABC/USBC was shot by collegiate bowler Jeremy Sonnenfeld in 1997 at Sun Valley Lanes bowling alley in Lincoln, Nebraska.
The first 900 in the history of the Professional Bowlers Association was bowled by Joe Scarborough on 22 April 2013 in a PBA50 Tour (formerly PBA Senior Tour) event. The PBA had seen 3 consecutive 300 games on one other occasion, by Norm Duke in 1996, but this was not considered to be an official 900 series because the games were not part of a contiguous set. The first two of Duke's 300 games were at the end of one round of play, and the third was at the beginning of the next round.
On January 11, 2017, John Buchanan III became the oldest bowler in USBC history to roll a sanctioned 900 series.