A “spoiler” is a non-winning candidate whose presence on the ballot affects which candidate wins. This one negative outcome of vote-splitting. Any non-viable or non-major candidate is often labeled as a potential “spoiler.” The most common example is a third party candidate competing alongside a Republican and a Democrat. Another example could involve a lesser-known city councilor entering a Senate primary dominated by two former governors. In both cases, the major candidate who will be hurt the most is the one who shares the most similarities with the new entrant.

Any similarity relevant to voters can cause vote-splitting. Here are some examples:

• Similar part of the ideological spectrum (i.e. both moderates)

• Similar policies

• From the same geographic place or community

• Similar elected positions or professions

• Same race, ethnicity or gender

"Spoiler" is mostly used as a pejorative term to insinuate that a person running should know they are hurting a shared cause. Historically, American voters either fear that new candidates will "steal votes" from their preferred candidate, or they want to support a third option but feel like they can’t. The spoiler effect is often cited as a limitation of plurality voting systems and has prompted discussions about electoral reform to mitigate its impact.

Approval voting stops the spoiler effect, as voters can support all the candidates they align with. This makes approval voting an ideal solution for promoting a diverse representation of people and values because it lets candidates run without worrying about ruining allies chances of winning.