1 - are the wheels tight? - Do you have any thrust when holding the plane up from the ground?
2 - are the fans spinning free? - Some (GWS) needs to be trimmed to get clear from the tube.
3 - Battery - does it give enough power. C-rating or cable gauge..
I can think of a few things that would cause that. A bad battery, or one that wasn't charged all the way. It could have been an older kit, and the motors aren't strong enough to take off from a grass field. The end points on the ESC aren't adjusted, so it doesn't spin up to full throttle like it should.
Most certainly does not sound right, he built this you say...scratchbuilt or kit? Not uncommon for folks unfamiliar with edfs to "egg" the housing a bit during assembly. If it was a edf kit and a cheaper one at that they are notorious for poor tolerances in foam mold around fan housing. Either too tight or too loose, if too tight its very plausible being new to all this he simply "crammed" the edf(s) in causing them to egg slightly thereby making the fan bind. I would remove both motors and bench test, if egging was the culprit simply remove a bit of foam.