There is another factor at play here: Rugby, Australian rules, and Gaelic league wear next to no equipment. The problem with American Football is the players ar

There is another factor at play here: Rugby, Australian rules, and Gaelic league wear next to no equipment. The problem with American Football is the players are geared up with heavily padded helmets. This has the effect of turning heads into battering rams. You wouldn't see 2 rugby players run into each other full steam because they don't have gear and would break bones and get cut. The gear lessens brain impact but does not eliminate it. So you then get higher impact forces that appear less brutal due to non visible trauma to the brain that is being rattled the whole time.