freewheel play (is normal to have some wobble but not too much maybe 1mm is ok). If it is large wobble you can replace the freewheel, or you can carefully adjust the play*.

*remove the wheel, lay it horizontal, remove the ring with two holes (in clockwise direction!), and WITHOUT LIFTING the gears, pick and remove one spacer washer you will find in there along with those lots of tiny balls that you want to stay in there. The key is to work slow and after removing the two-hole ring-cone thing the wheel should be kept at horizontal not to spill ball bearings, and do not touch the gears in an upward motion (it will come off and make a mess spilling a lot of balls/springs/pawls.)
After removing one spacer, reinstall the two holed cone-ring thing (counterclockwise!) and then check for play. If it's too tight add the spacer again (maybe a smaller spacer).. you get the idea.