Backing a youngster that runs

[lurcherlu]

It would be useful to have someone on the ground, but what I would do in this case is get him used to flexing his neck side to side by rein pressure, I would then lean over him flexing side to side, sit up a bit without feet in stirrups and 'rock around' a bit, again flexing his neck round if he becomes tense. I wouldn't be too quiet about leaning over him and try and move him around a bit.
When up I wouldn't ask him to go forward but flex his neck round and keep turning him on himself. He should be used to the 'neck flex' by this point. I have used this technique on youngsters who tend to rush off, you have more control and they can get used to you and movement without building up speed hopefully. I would try this in a round pen.

Btw ditto what GG said, I let the long lines drop and pull them gently round their legs, 'throw' saddles pads on and let stirrups bang around. When leaning over I pat the horses rump, shoulders etc and make a fuss. OFten horses panic because they don't quite realise how you got their or not 100% aware.

Get him to bend and then food reward I did this with mine and when I got n asked to bend round to my feet and take a carrot , when she walked on a couple stride asked for the bend again . Now I have a very sensible rising 5 who if has a moment of dou bt bends back to my foot for reassurance