I first became aware of the phrases "on the schneid" and "off the schneid" in the 1980s and 1990s in connection with baseball, where they meant, respectively, "enduring a string of bad performances" and "breaking out of a bad slump" (sometimes referred to as an "o-fer" when a hitter has not had a base hit in, say, 18 at bats over several games, making him 0-for-18).
Paul Dickson, The Dickson Baseball Dictionary, third edition (2011) has the following entries for schneid and schneider:
schneid A game, series of games, or period during which a team has been shut out or a batter has gone hitless.
schneider To shut out. ... ETYMOLOGY. According to Harold Wentworth and Stuart Berg Flexner (Dictionary of American Slang, 1960), the term came originally from the German and Yiddish "schneider" for one who cuts cloth, or a tailor. On its way to baseball, it appears to have become a gin rummy term for preventing an opponent from scoring a point in a game or match.
I have never seen or heard the term schneider used in the way Dickson describes, but I particularly remember (sometime in the late 1990s) the Oakland Athletics manager Art Howe expressing relief after his team finally won decisively, after a series of poor performances and a long series of innings during which the team had gone scoreless, that the A's had "gotten of the schneid." The Athletics' radio announcers used the term, too. The connection of baseball players to gin rummy is quite strong because gin rummy is one of the main card games traditionally played in major league clubhouses, a fact mentioned by players and sportswriters for decades.
Leo Cohen & Robert Scharff, Cohen's Complete Book of Gin Rummy (1973) [combined snippets] devotes considerable time to the subjects of being "on a schneid" and getting "off the schneid," since avoiding the former and becoming adroit at the latter are crucial to winning at gin rummy:
While getting off a schneid or keeping an opponent on a schneid are the most overriding situations in any game, most hands should be played to win the maximum number of points. Sometimes you can win more points with a "weak" knock than with a "good" gin. In such a case, play to knock as quickly as you can. At other times, you may determine that a knock would win very little. Then you should play the hand for gin.
The points system in gin rummy rewards winning hands in which the opponent is held below a certain number of points (as rogermue notes in his answer) at a much higher rate than it does ordinary wins.