I tried using my 35" sling as a mace today, only instead of a overhand knot I just used a carabiner clip that i keep handy on my belt
unable to find a rock, I used a walnut. The walnut was smashed. so was the spring on my clip
. ( I was able to get it back in place with a pair of pliers )
this actually seems like it would make a good last-ditch weapon. Even if one were to block it with a stick/mace, it could still swing around, possibly still hitting them or giving you a chance to knock their weapon out of their hands.
still, no good against swords or spears, or someone with a large shield.