Sorry to repeat my post from another thread but I thought this might help?
There is a law which relates to players equipment. This states that a player must be wearing Boots, Shirt, Shorts, Socks and Shinguards and that these items must be in good condition and not be a cause real or potential of injury to the player or an opponent.
There is also a law which states it to be an offence to indulge in conduct likely to endanger oneself or an opponent.
It seems that Chris lost his boot initially up by the Corner Flag in front of the Offices and was at that time instructed to put it back on. However he didn't do this immediately, instead continuing to play. Unfortunately the next time he was involved in play was in front of both the Referee and the Dug-outs hence the free kick and Chris having to leave the field of play to replace his boot. Having left the field of play he then has to wait until the referee allows him back on before he can rejoin play.
I discussed this last night with a Refereeing colleague who also happens to be an instructor and, like me, an examiner and it seems to us both that there was a transgression of both the areas of Law referred to at the top of my reply.
In law therefore the Referee was correct to do this but incorrect in not cautioning Chris.
Hope this helps
Phil