Hamstring Injury

I was trying to stop posting so much cause I know I do that but I really got hit hard today. I was going to go all out on my swings and see what I could do. I started to swing really calm and tight for maybe 2 rounds. At the early part of the 3rd round the inner part of my hamstring felt like it loosened up. The area cracked and gave a loosening sensation. Then the next swing I felt the pain and stopped right there. I put some ice on and my ETK video on and then proceeded to internally cry for about 45 minuets. It seems that I do the exact same thing as the video. I just go a little get my back a little lower. There is a picture of Pavel in the Russian kettle bell challenge with his back maybe slighty lower but he is obviously more flexible then me. Could it have been that I was over stretching my hamstring or can these things happen when your hamstring is too weak? I never heard of that. I was warmed up. It is the part of my hamstring right near my groin where my glute meets my hamstring.