Ring, cracked down on the ring

A match-fixing ring with more than 200 suspected members fixed or tried to fix around 200 matches across Europe, including three in the Champions League, in what UEFA called the biggest betting scandal in Europe.
Bochum state prosecutor Andreas Bachmann said at a news conference on Friday initial estimates put the illegal gains at about 10 million euros ($14.85 million) but he added that the figure was just "the tip of the iceberg".
Police in Germany, Britain, Austria and Switzerland cracked down on the ring on Thursday, staging simultaneous raids that resulted in 15 arrests in Germany and two in Switzerland.

source : http://in.news.yahoo.com/137/20091120/375/tsp-police-expose-europe-s-biggest-match.html

Please tell me the meaning of "ring" and "cracked down on the ring" in this context.
I feel "ring" means "a crime" and "cracked down on the ring" means "prevented a crime".