Many researchers make the differentiation between those who are aggressive  and those who are assertive on the sporting field.  “Aggression is behaviour with a goal of harming of injuring another being motivated to avoid such treatment”[1].  There is the idea of whether a participant is just being assertive.  A small difference when you are throwing your shoulder into a tackle to perform one of those crushing and utter defeats to a winger making a sprint down the sideline. (or something along those lines as I am lead to believe).  The main difference is in the intention – to harm or to achieve an outcome that is indirect to harm.