Well adrenaline is simply your fight or flight response. When your body becomes exposed to a stressful situation, or becomes under attack, you release adrenaline and other compounds which boosts your physical ability. The typical adrenaline response probably wouldn't make much of a difference in this type of setting, but your move is okay.
As you rear your head back, the attack plan becomes quite obvious. Waiting for the perfect moment I quickly duck down below the incoming head butt and coil my legs in anticipation for the follow up attack. As your head misses me, the momentum carries it forward and over my now crouched body. I spring myself upwards and drive my left palm up into the bottom of your chin, lifting you slightly off the ground. Without wasting a moment I pivot on my right foot spinning my body to my left and whip my left leg around planting my heel into the left side of your body, sending you falling to your right as you fall back to the ground.
Alright, since this is kenjutsu, lets try and keep the focus there. No more hands and feet, lets pretend these are real swords.