Just about any aspect of a century and a half of baseball can lay some claim to being old-fashioned. But for an announcer, writer, or fan, nothing is as old-fashioned as a pair of strong performances from a game's starting pitchers. I heard that cliche "We've got a good old-fashioned pitchers' duel" for the millionth time while watching the Cubs play the Diamondbacks last Friday, as Zac Gallen threw a nine-inning shutout for a 1-0 win, and I wondered, when did a pitchers' duel become invariably, ineluctably old-fashioned? Who was the first person to deem it to belong more to baseball's past than its present? Well ... it's complicated.
I searched through a bunch of old newspaper articles to try to glean an answer. It probably won't be surprising that "old-fashioned pitchers' duel" seemed to come into regular use as a phrase in the 1920s. For the first two decades of the century, baseball for a variety of reasons saw a steep drop in offense known now as the dead-ball era. But with the rise of Ruth, who all but invented the modern home run and smashed a mind-blowing 54 for the Yankees in 1920—more than any other team in the American League— the balance of power in an at-bat see-sawed back to the hitter. The use of "old-fashioned pitchers' duel," then, was used explicitly to contrast the light-hitting pre-Ruth days with the new age of the long ball.
"Of secondary interest was the remarkable pitching of Bob Shawkey," wrote the New York Herald in a 1920 Yanks–White Sox gamer, "Who had the better of Urban Faber in one of those old fashioned pitchers' duels which used to be the thing before hitting became so prevalent and popular. Babe Ruth's absence no doubt helped make it a flinger's frolic."
In a write-up of a 1927 contest between Rochester and Jersey City, The Bayonne Times' lede read, "An old-fashioned pitchers' duel, the kind that went out when the mighty Sultan of Swat set the style for free pill socking, was staged by Cliff Jackson and 'Lefty' Shoffner at West Side Park yesterday afternoon."
(As a quick side note, going through these archives was also a neat lesson in how much space newspapers used to give to baseball teams outside the "major leagues.")
From that decade on, the context for "old fashioned pitchers' duel" was established: There's a lot of slugging in the game today, but there was once a time when baseball was ruled unilaterally by the men who threw the ball. However, that's not where or how this saying began. The truly interesting history of the phrase begins well before Ruth ever sent one deep.