“Defense never slumps” (baseball adage)

“Defense never slumps is a baseball adage. Hitting can clump and pitching can clump, but defense is usually consistent.
 
“You know what they say: ‘Defense never slumps’” was cited in print in 1991. “Defense travels well” is a similar saying that has been used in both basketball and football.
 
     
Google Groups: rec.sport.baseball
Valentine
11/1/91
(...)
You know what they say: “Defense never slumps”.
 
10 March 1994, Augusta (CA) Chronicle, “Defense awakens for Paine” by Ed Price, pg. C1, col. 5:
GREENWOOD, S.C.—Defense never slumps, the saying goes.
 
23 April 1999, Dayton (OH) Daily News, “Cameron praised for work in center field” by Hal McCoy, pg. 6D:
“Defense never slumps. And I don’t subscribe to those who say whatever I hit will be a bonus.”
 
12 September 1999, Sacramento (CA) Bee, “Giants are getting defensive again,” pg. C5:
Giants manager Dusty Baker is fond of saying that “hitting and pitching slumps, but defense never slumps.”
 
Baseball Analysts
SEPTEMBER 08, 2009
Defense Never Slumps (Or Does It?): Estimating the Variability of Defensive Performance
By Sky Andrecheck
One of the oldest adages in baseball is that speed and defense never go into slumps.
   
The Wall Street Journal
April 8, 2013, 9:13 p.m. ET
Is Ruben Tejada a Gold Glover?
Four Errors in His First Five Games Makes It Seem Like No, but David Wright Would Argue Otherwise
PHILADELPHIA—An old baseball adage says that defense never slumps.

Try telling that to Mets shortstop Ruben Tejada. He committed four errors his first five games of the season, a stretch of sloppiness so baffling and dramatic that it rendered the Mets incapable of fathoming an explanation