a series of training games played by major-league teams before the opening of the season (so named because they take place in the citrus-growing South, as in Florida).
Origin
1950-55
Slang definitions & phrases for grapefruit league
grapefruit league
noun phrase
The association of major-league teams as they play each other in preseason training
[1937+ Baseball; fr the fact that most spring training camps are held in citrus-growing regions]