美式橄榄球,美式足球,橄榄球 both okay. we always said:橄榄球

美式足球(American football)

It depends the meaning of Football in your country. In China,足球 means soccer。A famous star ：David Beckham

美式足球 or 美式橄榄球 are both correct and exact. 橄榄球 is correct but not exact because rugby is 橄榄球 too. The thing is that most Chinese people don't familiar with 橄榄球, so we can't tell American Football from rugby. That's why they are both called 橄榄球 here.

"American Football" :在中文裡是指"美式足球or美式橄欖球". "football" :在中文裡是指"英式足球".For ex.:FIFA. "soccer" :在中文裡是指"英式橄欖球".