That rule existed in horse racing before most of us knew what a liberal was. My Dad owned a few race horses when I was a kid; so I got to spend a lot of time at the track. I was too young to be allowed in the stands where parimutuel betting took place; but I was allowed in the stables. During actual races I could watch from the trainer towers in the stable area.
I remember watching one race in particular at Gulfstream Park in Hallandale Beach, FL. A similar lane change took place with much worse consequences. The rear legs of the lead horse got tangled up with the front legs of the horse that got cut off. Three horses went down coming out of the turn just below the tower where I was standing. Two of the horses got back on their feet; but the third had a broken leg and couldn't get up. The track Vet came out and examined the horse. Then some guy came out and shot the horse in the head with a pistol. They hooked the dead horse's rear leg to a tractor and drug it off the track so the races could continue. It wasn't something easy for me to watch as an eleven year old kid.
I imagine in today's world the horse would be put down with a lethal injection; but things were done a little differently in 1948. Anyway, situations such as that is why we still have the rule about lane changing in horse racing. It took guts for the officials to call the violation in a race as big as the Derby; but their call was the correct one.
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