tr | letters to symbol, bash scripting

Shell Programming and Scripting
1

hi Im trying to make the 'response' return the answer in the form of a dash (-) rather than the actuall letters of a given word typed in, this is what i have tried, but im not getting the dashes come through just a blank screen, any ideas guys?

function enterWord () {
echo "select to be player 1 or 2"
read player

echo "player $player enter a word"
read response

clear
}

function readResponse () {
echo "$response | tr [a-zA-Z][_]"
}

enterWord
resp=$(readResponse)
echo "player $player your word was $resp"

2 
echo $response | tr '[a-zA-Z]' _
3

works fine, thanks very much!