Production was halted for weeks after Walter Matthau had a heart attack. He had slimmed from 190 to 160 pounds by the time filming was completed and wore a heavy black coat to conceal the weight loss.

This was director Billy Wilder's second film in a row in which one of his lead actors suffered a heart attack. In his preceding film, Kiss Me, Stupid (1964), Peter Sellers' health problem forced Wilder to replace him with Ray Walston. In this film, Walter Matthau suffered his attack midway through production, but shooting was postponed until he recovered. His drastic weight loss from scene to scene is noticeable.

Jack Lemmon and Walter Matthau bonded early in the production process, finding a connection in their mutual love of football. They would remain friends the rest of their lives.

Marked the first pairing of Jack Lemmon and Walter Matthau, who subsequently worked together on 11 additional films (including Kotch (1971), in which Lemmon directed Matthau).

This is the first film on which Billy Wilder and Walter Matthau worked together, though Matthau was Wilder's first choice for the part in The Seven Year Itch (1955) that was played by Tom Ewell.

Continuity

During the football game in which Harry is injured, the Browns are playing the Minnesota Vikings. On Boom-Boom's punt return, however, the opponents are the Philadelphia Eagles.

When Harry is injured, his camera flies out of his hands, and the cables are missing. In the previous scene, the cables were shown attached using a screw-in type connector that would not have come off, even when being tackled.



Factual errors

When the "stop-action replay" of Harry's accident is shown, the camera is focused on Harry for a second or two before Boom Boom hits him. In reality, the camera would be following the action on the field and would not be focused on Harry, since the director and camera operator would not have known in advance that Boom Boom would hit Harry. Harry would not have come into view until after Boom Boom is knocked out of bounds.

Just before being hit on the sidelines by Boom Boom, Harry is shown without his headphones on. A cameraman wouldn't keep his job long if he didn't stay in touch with the director at all times.



Incorrectly regarded as goofs

Keith Jackson never called NFL games for CBS. However, in the credits he is listed as "Football Announcer", not as himself, so this is not necessarily a mistake.

Early in the movie, a poster showing the Browns schedule appears. The Washington Redskins are listed as the opponents for a game on December 5. However, later in the movie, mention is made (in connection with the planned Harry Hinkle Charitable Fund announcement) of the game against Washington being scheduled for November 27. However, this is not necessarily a goof as the two teams played twice a season (home and away) for years through 1966.



Audio/visual unsynchronized

Near the beginning of the movie when Harry is wheeled out after his X-ray, his mother is crying over him. But more than once she can be heard sobbing, even though she's just standing still and looking at him.



Crew or equipment visible

Reflected in the apartment window when Harry is holding the candle.