Rock Paper Scissors without arrays and if-statements, how to reduce
This will do

int a = _random.Next(0, 3);
int b = _random.Next(0, 3);
int winner = (a - b + 4) % 3 - 1;


There is no need to subtract angles in radians or degrees as you can simply use integers. Technically a - b is sufficient to determine the winner and + 4 % 3 - 1 wraps it to the -1/0/+1 interval.