A political election is “too close to call” when it’s not certain who will win. Marty Plessner (1926-2014), a political director at CBS News, said that CBS coined “too close to call” in its election coverage in the early 1960s.
 
However, “South Dakota: It’s too close to call, Republican experts say” was cited in print in 1950. The phrase “too close to call” was used much earlier in sports, such as boxing.
   
 
Wikipedia: Marty Plissner
Martin P. “Marty” Plissner (May 20, 1926 – February 6, 2014) was an American political commentator. He worked for CBS News from 1964 until his retirement in 1996.
 
He first began his job during the United States presidential election, 1964 during Robert F. Kennedy’s campaign. He was known for coining the phrase “too close to call”.
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“Too close to call”
In the early 1960 elections, there were no exit polls to predict the outcomes. A model was devised, based on certain reported-precinct results, which gave samples for mathematical formulae to be applied. In one unspecified situation, all the votes were reported but there was no clear winner, Plissner and his CBS newsteam called that election “too close to call”.
   
3 June 1950, El Paso (TX) Herald-Post, “Inside Washington—A Weekly Sizeup,” pg. 4, col. 3:
South Dakota: It’s too close to call, Republican experts say.
 
5 January 1955, Florence (SC) Morning News, pg. 1, col. 3:
Soil District Election
Is too Close To Call
 
12 October 1958, Boston (MA) Sunday Herald, “Statistics Favor Democrats” by Douglas B. Cornell (AP), sec. IV, pg. 19, col. 2:
MINNESOTA—The Senate struggle between Republican Sen. Edward J. Thye and Democratic Rep. Eugene McCarthy looks too close to call.
 
4 November 1958, The Times-Picayune (New Orleans, LA), “Contests in East Tabbed as Likely to Show Trend” by the Associated Press, pg. 5, cols. 2-3:
NEW JERSEY—Also close—too close to call between Harrison A. Williams (D) and Robert W. Kean (R) for a seat now held by the GOP.
 
24 APril 1960 Dallas (TX) Morning News, “West Virginia Editors See Humphrey as Victor (New York Times), sec. 1, pg. 3, col. 4:
Eleven forecast a state-wide Humphrey victory, four thought Kennedy would win, and nine others either thought the race was too close to call or said they had no opinion on the outcome.
 
New York (NY) Times
ON LANGUAGE; Too Close to Call
By William Safire
Published: June 23, 1996
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Too close to call, as best I can tell, comes from political broadcasting. Since 1647, a call has meant a judgment, and it was popularized after the 1860’s by baseball. (A strike is called by an umpire, who also calls a sliding runner out or safe and calls a game on account of rain.) Daniel Schorr of National Public Radio remembers the phrase from the early days of television, and directed me to Martin Plissner of CBS, a pioneer of electronic election coverage.
 
“That phrase was invented at CBS between 1962 and 1964,” says Plissner with the confidence never shared by lexicographers. “During that period, instead of using the exit polling we have today, we used a model we had devised for predicting or calling elections based on certain reported-precinct results. That gave us a sample to which we could apply mathematical formulae to determine a call. When we had a situation in which all the votes were reported but there was no clear winner, we called that election too close to call.”
     
Politico
Marty Plissner, longtime CBS News political director, dies at 87
By ADAM CLYMER | 2/6/14 7:44 PM EST
Marty Plissner, the longtime political director of CBS News who coined the phrase “too close to call,” died Thursday. He was 87. The cause of death was lung cancer.
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His coinage of the phrase “too close to call” was noted by William Safire of the New York Times, in his June 23, 1996 “On Language” column.
 
Safire quoted Plissner as saying the phrase was first used at CBS in the early 1960s: “During that period, instead of using the exit polling we have today, we used a model we had devised for predicting or calling elections based on certain reported-precinct results. That gave us a sample to which we could apply mathematical formulae to determine a call. When we had a situation in which all the votes were reported but there was no clear winner, we called that election too close to call.”