WhoWins™ defines an "annihilation" as a 4-game series sweep in which the swept team never -- not for even one second -- holds a lead. In MLB and NHL series, annihilations can be defined in the true sense, since we have access to game scores after every half-inning in MLB play, and every second in NHL play. In NBA series, since we do not have access to game scores every second, we can define an NBA "pseudo-annihilation" in which the swept team never holds a lead at the end of a quarter during the sweep. Interestingly, the percentage of sweeps that are annihilations or pseudo-annihilations is on a par with the percentage of best-of-7 playoff series that are sweeps.

In 1550 best-of-7 series through 2023:
31 of 191 MLB best-of-7 series ended in sweeps (16.23%), and 7 of those 31 sweeps were annihilations (22.58%)
92 of 603 NBA best-of-7 series ended in sweeps (15.26%), and 9 of those 92 sweeps were pseudo-annihilations (9.78%)
128 of 756 NHL best-of-7 series ended in sweeps (16.93%), and 19 of those 128 sweeps were annihilations (14.84%)

MLB Annihilations (Annihilator (vs. Annihilated)):
1963 Finals (World Series): Los Angeles Dodgers (vs. New York Yankees)
1966 Finals (World Series): Baltimore Orioles (vs. Los Angeles Dodgers)
1989 Finals (World Series): Oakland Athletics (vs. San Francisco Giants)
2004 Finals (World Series): Boston Red Sox (vs. St. Louis Cardinals)
2012 Semis (League Championship Series): Detroit Tigers (vs. New York Yankees)
2015 Semis (League Championship Series): New York Mets (vs. Chicago Cubs)
2019 Semis (League Championship Series): Washington Nationals (vs. St. Louis Cardinals)

NBA Pseudo-Annihilations (Annihilator (vs. Annihilated)):
1959 Finals: Boston Celtics (vs. Minneapolis Lakers)
1971 Finals: Milwaukee Bucks (vs. Baltimore Bullets)
1980 Qtrs: Boston Celtics (vs. Houston Rockets)
1982 Qtrs: Los Angeles Lakers (vs. Phoenix Suns)
1987 Semis: Los Angeles Lakers (vs. Seattle Supersonics)
1991 Semis: Chicago Bulls (vs. Detroit Pistons)
2008 Prelim: Los Angeles Lakers (vs. Denver Nuggets)
2012 Prelim: San Antonio Spurs (vs. Utah Jazz)
2013 Prelim: San Antonio Spurs (vs. Los Angeles Lakers)

NHL Annihilations (Annihilator (vs. Annihilated)):
1946 Semis: Montreal Canadiens (vs. Chicago Blackhawks)
1952 Finals: Detroit Red Wings (vs. Montreal Canadiens)
1954 Semis: Montreal Canadiens (vs. Boston Bruins)
1960 Semis: Montreal Canadiens (vs. Chicago Blackhawks)
1960 Finals: Montreal Canadiens (vs. Toronto Maple Leafs)
1969 Qtrs: Boston Bruins (vs. Toronto Maple Leafs)
1969 Qtrs: St. Louis Blues (vs. Philadelphia Flyers)
1977 Qtrs: Montreal Canadiens (vs. St. Louis Blues)
1978 Semis: Montreal Canadiens (vs. Toronto Maple Leafs)
1979 Qtrs: New York Islanders (vs. Chicago Blackhawks)
1987 Prelim: Detroit Red Wings (vs. Chicago Blackhawks)
1989 Prelim: Pittsburgh Penguins (vs. New York Rangers)
1992 Qtrs: Chicago Blackhawks (vs. Detroit Red Wings)
1995 Qtrs: Detroit Red Wings (vs. San Jose Sharks)
2000 Prelim: Detroit Red Wings (vs. Los Angeles Kings)
2009 Prelim: Detroit Red Wings (vs. Columbus Blue Jackets)
2013 Semis: Boston Bruins (vs. Pittsburgh Penguins)
2015 Qtrs: Chicago Blackhawks (vs. Minnesota Wild)
2021 Qtrs: Montreal Canadiens (vs. Winnipeg Jets (II))

Noteworthy notes:
During the annihilation of San Francisco by Oakland in the 1989 MLB World Series, an earthquake devastated San Francisco just before Game 3 of that best-of-7 MLB Finals-round series. After a delay, Games 3 and 4 of that series were played in San Francisco; in each of those games, Oakland established leads in the top of the 1st innings that the Athletics would never relinquish. After the earthquake, the San Francisco Giants did not enjoy so much as a single plate appearance in which they were even tied with the Athletics (let alone in the lead) . . . During the 1960 NHL playoffs, the Montreal Canadiens used two consecutive annihilations to win their fifth consecutive Stanley Cup; their opponents never once led Montreal during the entire best-of-7 playoffs in 1960 -- an apparently unprecedented demonstration of dominance that has yet to be repeated . . . As has been shown elsewhere on this site, the 1969 annihilation of Philadelphia by St. Louis in the NHL Quarterfinals round saw the Blues with leads of two or more goals over the Flyers for almost 75% of the duration of that best-of-7 series -- thus underscoring the one-sidedness of that series . . . During the annihilation of St. Louis by Boston in the 2004 MLB World Series, the Boston Red Sox not only had never trailed in the series, but also had held a lead at some point in each and every inning of that series -- an unprecedented accomplishment in the history of MLB best-of-7 playoff series.