Definition of I-formation in English:

I-formation

noun

  • 1American Football
    An offensive formation in which the quarterback and two or more running backs (typically a fullback and a tailback) form a line behind the ball, at right angles to the line of scrimmage.

  • 2Tennis
    A formation in doubles matches in which the server stands close to the centre mark on the baseline and his or her partner stands close to the centre service line.

Origin

1950s; earliest use found in The Newport Daily News.