Push starting a brushed motor?

I picked up a duratrax evader for the wife (I have a T4 she wanted to bashed with me once). I have noticed sometimes it seems to like to be push started, aka the motor will not move the vehicle unless someone pushes it alittle, it will not start from an unmoving position.
She is currently running a 27T stock brushed motor and a VXL ESC (had it sitting around).
What would be the likely culprit? Bad ESC? Bad Motor? Bad Battery? I am guessing/hoping it is the motor, just wanted some other opinions first.

Thanks