Blackballing, ostracizing someone socially, e.g. prevention of finding local or field-specific employment, blacklisting from a club or other organization, etc.
Blackball, New Zealand, a small town located on the western coast of the South Island of New Zealand; see also Blackball Branch in the "Transportation" section, below.
Games and sporting
Blackball (pool), a variant of the pocket billiards game eight-ball, sanctioned by the World Pool-Billiard Association and popular in the UK and Australia among a few other places
The black ball in pocket billiards games including pool and snooker
Blackball, a pejorative term used to represent the Black baseball movement including the formation of Negro league baseball
Blackball, a monster in the Mystara campaign setting of Advanced Dungeons & Dragons
Blackball (surfing), a nickname for the letter i flag among the international maritime signal flags, featuring a black solid circle on a yellow background, and having specific additional meanings in certain contexts ("no surfing allowed in this area" at lifeguarded beaches, "no diving allowed in this area" at swimming pools, "gale warning" in a harbor, etc.)