Use "had" as it is the safer choice. "Have" can work if you know for a fact that the players still (at the time of writing) have the disease.
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CalifJimI'd use "have" because as far as I've heard, that disease never goes away. That's probably why it's got the word "chronic" as part of its name.CJThat's a fair point, assuming the players are still alive.
teechrassuming ... still aliveYikes! Another fly in the ointment!
lucas21cIf all of them already died of the disease, then is "A recent study found that 87 out of 91 former NFL players have a brain desease called CTE, chronic traumatic encephalopathy" wrong?Yes. Use "had" in that case.