In some parts of the world football is very attractive to criminals. There is a lot of money in football and this is strong motivation for organised crime. In eastern Europe the 'mafia' is said to control a number of football teams and in South East Asia illegal gambling organisations have damaged the credibiltiy of their local football leagues. Players who might earn comparatively little can increase their income by taking money from people who want to get a certain result.
Obvious corruption has a negative effect on the game.
Sponsors are less likely to support a team, players can lose motivation and fans can lose interest.