The advancing blade has more speed thus generate more lift for a given collective take, while the retreating blade is slower and loses lift capabilities.
Forces are applied like you said 90º offset, so you have lift in the nose and drag in the tail. The helicopter will pitch up and then roll to the side where lift is lost.
I hope I am not making any wrong statement. There are probably more experienced pilots around here that might have real RBS experiences and can help more than me.
Take care.