This is at least a quarter's worth, Dan, so listen up.
I don't have a problem with a truck tow ball as a TIP, it's probably much stronger than your rope. It is round and won't cut the rope, either.
Unfortunately, it is rather smooth. Polished, in fact. Everybody knows that a clove hitch relies on the friction of the wraps and the non-rolling stability of the "branch" to prevent unrolling.
In case you didn't know it, a clove hitch is nothing more than a 1/2 hitch (or an overhand knot) with an additional 1/2 wrap. If you don't think so, unwind a clove hitch 1 turn and see what you are holding.
I am sure that you wouldn't tie an overhand knot on that ball, so why use the clove hitch ? It is pretty darn easy to add one more 1/2 hitch, and then you would have had a reliable knot.
You could also have added a stopper knot to that clove hitch, and it would have been better. Even the old fashioned "taut line hitch" friction knot was little more that FOUR 1/2 hitches, and it requires a stopper knot to be safe.
We're glad you are fine, but please use a better knot next time.
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Yes. Cute kid. Looks kind of like my two, just younger. They are graduating from cute and getting into "pretty". Before long, I anticipate "beautiful", and that comes with Beaux (boyfriends)