I think in full contact, American Kickboxing around that time, it wasn't allowed to kick to the leg all together as it was considered too easy and trashy....like spamming. Then this fight happened where the Karatekas/Kickboxers agreed to let a Nak Muay kick to the leg (although I doubt they allowed full Muay Thai....so no clinch, knees nor elbows):
I read that despite Rick Roufus' brother talking mad trash about how cheesy it was during the interview right after, their whole camp went out ASAP to train Muay Thai techniques.