Arrowhead Brass 450 Series Leaking From Behind The Wall
If the water is coming from behind the wall, that means that the faucet most likely split due to water being left inside the faucet when the temperature got below freezing. If the faucet is split, then it will have to be replaced. To replace the faucet, there will be 2 things you need to know. First thing would be to know the wall thickness. To find the wall thickness you can take the stem out of the faucet and measure it from end to end.
Once you have that, you can subtract 4 inches from it to find the thickness. For example, if your stem measured 10" from end to end, that would mean you have a 6" wall thickness. Next thing you would want to know is how it connects to the main plumbing. There are many connection types, so you would need to know the connection size, and how it connects so you can get the correct replacement faucet.
See below to help find the correct stem
See below to find the correct connection your faucet uses