The statistic that they never give you is that 100% of fights start standing up. That sounds silly, but it is very vaild to understand that point.
I work as a Corrections Deputy for a Sheriff's dept. that houses around 550-600 inmates. They range from not paying child support all the way up to murder. I have seen alot of fights and unfortunatly been in alot of them as well. Here is what I have learned from MY observations.
1) Inmate vs. inmate: Only a couple went to the ground because one inmate picked up another one and threw him down. The only time I have seen it go to the ground other than that is because of environmental factors, such as, tripping on a chair
2) Inmate vs. guard: Just about every one of them goes to the ground because we have to hand cuff them.
I have never seen a single leg, double leg takedown before in any of these fights. They were either picked up and thrown straight down. Or taken down from officers with an ikkyo type technique. I hope this helps out some, as far as fights go.