Zebra (sports official who wears a black-and-white-striped shirt)

NFL officials’ uniforms and NHL officials’ uniforms have black-and-white-striped shirts, like a zebra’s stripes. The officials wearing such shirts are often nicknamed “zebras.”
 
“Frankly, NFL officials disappoint me. As bad as it is, however, I’m a law and order man so must abide by the Zebras’ decisions” was cited in print in October 1969. The “zebra” nickname became popular in the 1970s.
 
 
26 October 1969, The Times-Picayune, “Behind The Sports Scene” by Bob Roesler, sec. 6, pg. 2, col. 1:
Frankly, NFL officials disappoint me. As bad as it is, however, I’m a law and order man so must abide by the Zebras’ decisions.

7 January 1971, The Times-Picayune (New Orleans, LA), “Behind The Sports Scene” by Bob Roesler, sec. 3, pg. 5, col. 1:
If the friendly bet doesn’t get Mason in Rozelle’s doghouse, what he has to say about National Football League officiating might. So, when Tommy voiced criticism of Pete’s “Zebras,” I asked him if the statement was off the record.
     
4 November 1975, Morning Advocate (Baton Rouge, LA), pg. 4-C, col. 3:
NFL’s “Zebras” Taking Heat
Is It a Cheap Shot if You Don’t Get Caught?
By DAVE BRADY
The Washington Post
WASHINGTON—When football game officials come into high profile in Los Angeles, those in the trade use the expression, “The zebras have got us.”
 
The allusion, of course, is to the spoilsports in the striped shirts, whose lot is not a happy one in trying ti keep the violence in reasonable control.
 
Sports Illustrated
January 10, 1977
Which Team Has The Better Airport?
Before departing for Super Bowl XI, pro football writers Dan Jenkins and Robert F. Jones debated the merits of Minnesota and Oakland.
(...)
OFFICIALS
Dan: The key to the game is whether the zebras call holding on Oakland. Last year we hear there was a mutual agreement, worked out by either Pittsburgh and Dallas or the NFL and CBS, or all of them, not to have any holding calls—and there weren’t any. The idea was to have a good game. If a zebra doesn’t decide this game, it will be the first one all season.
 
Sports Illustrated
October 09, 1978
It’s Open Season On The Zebras
NFL officials have routinely botched up games this season with quick whistles and questionable calls, but Pete Rozelle insists that his men get them right 95% of the time. Tell that to Minnesota Coach Bud Grant
William O. Johnson
 
Urban Dictionary
zebra
(n) common slang term for referees or field officials in certain sports (particularly in American football) due to the white and black striped uniforms
(...)
by methodmadness Mar 17, 2004
 
Google Books
Cassell Dictionary of Slang
By Jonathon Green
London: Cassell
2006
Pg. 1562:
zebra n.
(...)
3 [1970s+] (US) a stripe-shirted sports umpire.
 
Sports Illustrated
October 08, 2012
American Zebra
FOLK HERO, TWO-TIME SUPER BOWL REF, OWNER OF THE MOST FAMOUS GUNS IN THE NFL. THEN ALONG CAME THE LOCKOUT AND ED HOCHULI BECAME SOMETHING ELSE, AT LEAST IN THE TWITTERSPHERE: THE MOST IMPORTANT MAN IN FOOTBALL
Steve Rushin