Since the Death Eaters seem to be the topic du jour, according to Goblet of Fire, approximately 100,000 witches and wizards attended the Quidditch World Cup (Chapter 8 - pages 88 and 98 - (UK) - The Quidditch World Cup)
Now my math skills are even worse than J.K. Rowling's, but it seems that between seven and sixteen Death Eaters were responsible for the kerfuffle. How is it that 100,000 +/- individuals, as well as the entire Ministry of Magic (GoF - page 115 - (UK) The Dark Mark), including the Department of Magical Law Enforcement, could not corral sixteen Death Eaters and keep them from rioting and engaging in the torture of Muggles?
Here's how I came up with a guesstimate of seven to sixteen Death Eaters. The Death Eaters identified in the chapter The Death Eaters in Goblet of Fire are:
- Barty Crouch Jr. (Stayed at Hogwarts during Voldemort's return/Acted alone at the Quidditch World Cup)
- Avery (Jr. or Sr.?)
- Lucius Malfoy
- Walden Macnair
- An unknown number of other Death Eaters
It doesn't seem the number of Death Eaters at the graveyard was very high. The remaining Death Eaters who might have been present are Alecto and Amycus Carrow, Thorfinn Rowle, Yaxley, Jugson, Selwyn, Wilkes, and Gibbons.
Igor Karkaroff defected and fled. We all know about Snape. Bellatrix Lestrange, Rodolphus Lestrange, Rabastan Lestrange, Antonin Dolohov, Augustus Rookwood, Mulciber (Jr. or Sr.?), and Travers are in Azkaban at the time of the Quidditch World Cup.