What else did they do?
Also, are they any distant relation to Sinclair Oil? I listen to a ton of olde tyme radio and they are always advertising on 30s shows. Their ads are great because they are always opposing their clean, dependable service to "independent gas stations," conjuring Route 66 abandoned, gangster-infested, Ma and Pa Kettle rat traps where the crazy uncle will pee in the tank or abduct your daughter.
Sinclair Broadcasting has zero relation to Sinclair Oil.
As for screwing up their properties, the best example would be Ring Of Honor Wrestling. In 2018 ROH had grown in popularity thanks to a general dislike of the WWE product among wrestling fans, a partnership with New Japan Pro Wrestling, and the popularity of wrestlers like The Young Bucks (Matt and Nick Jackson), Kenny Omega, and Cody Rhodes (and his wife Brandy), all members of a group called The Elite (and a subgroup of the Bullet Club but I'm not going into that). They wanted more investment into ROH from Sinclair so ROH could continue to grow but Sinclair refused, they saw ROH as only a cheap program they could distribute to their local stations.
On a bet from Dave Meltzer (who runs the famous Wrestling Observer Newsletter), that came about after he said no non-WWE promotion could have a 10k+ attendance show, the guys in The Elite (plus others) ran a show
themselves in September 2018 called All In. It was a huge success, sold over 10k tickets and had a huge PPV buy. So what happened? The Elite left ROH, partnered with the Khan family (owners of the Jacksonville Jaguars and Fulham) and formed All Elite Wrestling. In under two years AEW went from nothing to a weekly TV show on TNT that draws nearly 1 million viewers (and would be rivaling WWE Raw in numbers if WWE wasn't counter programming NXT against them).
Sinclair had a golden opportunity to make big money and basically let it go for free. AEW has been growing huge, in spite of a pandemic, and looks to be cornerstone in Turner and AT&T's future plans while ROH is basically dying on the vine with wrestlers finishing out their contracts so they can sign with someone else.