When San Francisco Giants pitcher Matt Cain threw a perfect game Wednesday night at San Francisco’s AT&T Park, the Giants, per baseball tradition, converged upon the pitcher’s mound to celebrate the achievement. Twitter exploded with bad puns (“Cain is able!”). ESPN’s “SportsCenter” had a new lead story. Newspapers reconfigured the front pages of their sports sections.

But beneath all the appropriate bows to one of the sports world’s most riveting individual achievements was a strange realization: Perfect games and no-hitters sure do seem to be regular occurrences these days.

Indeed, Cain’s perfect game may have been just the 22nd in baseball history, but it was the second since the start of this season↓ (Philip Humber of the Chicago White Sox threw one in April), and the fifth since July 2009. (A potential sixth, by Detroit’s Armando Galarraga in 2010, was ruined by an egregiously blown umpire’s call on what would have been the 27th and final out.) Going back a little further, half of all the perfect games in history have come in the past 24 years.

If we expand the sample to include all no-hitters, Cain’s was the second in baseball in the past five days, the third this month and the fifth since the start of the season. The last time there were five no-hitters pitched before mid-June? Try 1917. With 3½ months left in the season, 2012 has a chance to surpass the all-time record of seven no-hitters in a single season, set in 1990 and equaled in 1991.

“There are just so many doggone good pitchers in the game, and I hate to say it, but maybe there are just fewer great hitters,” said former Washington Senators ace Dick Bosman, whose 1974 no-hitter for the Cleveland Indians is the only one in history in which the only batter to reach base did so on the pitcher’s own error. Bosman was also a big-league pitching coach for 11 seasons, and since 2002 has worked a roving pitching instructor for the Tampa Bay Rays.

Time was, perfect games were exceedingly rare. Don Larsen’s famous gem for the New York Yankees in the 1956 World Series was the first in baseball in 34 years. In the National League, Jim Bunning’s 1964 perfect game for the Philadelphia Phillies broke a spell of 84 years without one.

But suddenly, seemingly everyone is throwing one — and not just stars such as David Wells (1998), Randy Johnson (2004) and Roy Halladay (2010), but also less accomplished pitchers such as Dallas Braden (2010) and Humber.

Is there something going on here? Not necessarily. Baseball history is full of strange clusters of similarly exceptional performances. There were four Triple Crown winners between 1933 and ’37, but only five since. Another example: All six individual seasons of 62 or more home runs came between 1998 and 2001.

Then, too — thanks to expansion that has seen the league grow from eight teams to 30, and the lengthening of the season from 154 to 162 games — there are almost twice as many games in a major-league season (and thus, twice as many opportunities for historic individual feats) as there were as recently as 1960.

But just as the cluster of epic home run seasons around the turn of this century might be explained by the effect of steroids on the game during that period of juiced offensive numbers, the answer to the perfect game question might be found within a larger statistical trend in the game.

Simply put, batters are striking out at a rate never before seen. Through Wednesday’s games, that rate was 19.6 percent of all plate appearances, a full percentage point higher than the previous record of 18.6 percent, set last season. In fact, each of the past four seasons has seen a new record set.

By comparison, in 1968, commonly referred to as the “Year of the Pitcher” (but which, nonetheless, produced only one perfect game, by Oakland’s Catfish Hunter), batters struck out in just 15.8 percent of all plate appearances. As recently as 1981, that figure was 12.5 percent.

A higher strikeout rate, of course, means fewer balls being put into play, which means fewer opportunities for would-be no-hitters and perfect games to be lost via base hits or errors.

Batters “are still swinging from their heels with two strikes,” said Leo Mazzone, the former pitching coach for the Atlanta Braves and Baltimore Orioles. “It used to be, guys would choke up and protect the plate with two strikes, but now there doesn’t seem to be the same sort of stigma about striking out.”

Mazzone also believes since the ban of steroids and amphetamines in baseball, everyday players have less energy on a daily basis. “There’s a little bit of a fatigue factor now,” he said, “because the [drug] rules are what they are.” Starting pitchers, who typically pitch every five days, are presumably less affected than are everyday players by the tougher drug standards.

Nowadays, it seems, hardly a day goes by where someone isn’t flirting with a no-hitter in the late innings — or even after the game. On the same night as Cain’s perfect game, New York Mets knuckleball specialist R.A. Dickey pitched a complete-game one-hitter, with the only hit coming on a high chopper to third base that was ruled a base hit by the official scorer after third baseman David Wright failed to make a charging, bare-handed play.

After the game, the Mets protested the scorer’s decision, petitioning MLB to change the hit to an error — and thus credit Dickey with a no-hitter. Although such a scoring change would be unprecedented in such a circumstance, it would, in the context of this season, be completely fitting.