Beginner in Unity - 2d platform controllers how to roll the character?

Hello, I'm beginner in unity and I watched this video about 2D CHARACTER CONTROLLERS link: https://unity3d.com/pt/learn/tutorials/modules/beginner/2d/2d-controllers, because i'm trying to do a 2d game.

For now I have done the controllers showed in the video but with no Idle because my default state it's only Run. I created another state with the sprite roll (robot boy) connected to my default state and when I run the game they show the two (run and roll) animations at the same time. What I want to know is when the key "downArrow" is pressed the animation roll is executed but only when the key is pressed, I have just script the code to the key like it's made in the video for jump state.

My question is how i can make this work because I don't know how to do the script for this state. Please help me I appreciate.