do a 180 degree turn
To make a big change in some area of one's life. If one physically turns 180 degrees, one will then be facing the opposite direction. A: "Can you believe that Sam quit his job at the firm?" B: "No, he really did a 180 degree turn on being a paralegal!"
do a 180
1. Literally, to begin moving in the opposite direction. (If one physically turns 180 degrees, one will then be facing the opposite direction.) I was going to go to the park, but when I saw those dark clouds roll in, I did a 180 and headed back home.
2. To make a big change in one's position, opinion, lifestyle, etc. A: "Can you believe that Sam quit his job at the firm?" B: "No, he really did a 180 on being a paralegal!"