Yeah, it is very difficult to not injure the attacker in Aikido. It is actually part of the training to learn how to not hurt your opponent. There are various techniques that are not normally shown in the movies that can bring down an opponent before he even gets a chance to land a blow. A punch or an attack with a knife is Aikido 101, then the cool stuff gets taught. BTW, Bruce Lee didn't know Aikido. It is one thing to make a MMA fighter brawl with boxing rules, but entirely different the other way around.