Answer:
Until I am measured I am not known, Yet how you miss me when I have flown.
Do what he says and you'll be fine, don't and you lose the game.
Stealthy as a shadow in the dead of night, cunning but affectionate if given a bite. Never owned but often loved. At my sport considered cruel, but that's because you never know me at all.
I always run but never walk, I sometimes sing but cannot talk, No head on which a hat to place, You always look me in the face.
Different lights do make me strange, thus into different sizes I will change
I have two eyes in the front and a lot of eyes on my tail