This thing is O.P. Use "C" for single target mode. When you are surrounded by many dinos, just trust me, hold right mouse button that will take care of everything. Best idea would be go with stamina and meele.
Get a wyvern or quetzal and pick the velonasaur up and bring it into a taming pen. If both are not available and you dont have the power to kill nearby dinos, make a trap out of 4 wooden or stone gateframes and gates (add the gate doors to the gateframes otherwise it will escape)
Little late but... if you build a 1x1 (3 walls 1 door) then add a doorframe ontop of each wall and a ceiling ontop of that you have a reverse taming pen! Stand inside and agrro it and wait for it to be able to be shot through the doorframes. It cant shoot you but you can shoot its head. Easy tsme!
Get a friend with a good riot or metal shield to tank it while you knock it out with a good long neck or shocking tranq darts...it was an easy tame for us, but if you use shocking darts, you have to transfer them over so just use a good longneck.
Try a decently high level snow owl with stats invested in health and stam set to passive stay no wander, land right in front of the vela you wish to tame getting aggro on the owl then tranq, tame, and cryo the vela keeping an eye on your owl the entire time, if they get too bloodyvyou can always hop onto the owl and freeze up for a heal on both you and the wild Dino making it less likely for both creatures to die without affecting the torp too much
If you play by yourself you can tame a velonasaur by using a tranq creature and tranqing it while constantly moving in circles to dodge its needles or by being on a rock/small cliff then tranqing it In my first time taming one I was on a cliff and the velonasour couldn't attack me I was using a slingshot so it was hard.one last way to tame it is to use a tanky creature and tranq it while your dino is risking his life