Derby, a 23-year-old pitcher, and his family are all country music fans; they often travel to Nashville to see concerts. His group separated early during the concert. His parents took his 6-year-old nephew to see a Beatles tribute show at The Mirage, while his sister and brother-in-law stayed back in a grassy area. The rest of the group, including Derby, was about 100 yards from the stage.
• Vegas tragedy hits home for players, ex-players
"My parents decided at the last minute that they wanted to take my nephew to The Mirage to watch the Beatles show," he said, "which was way out of the way of everything that happened. My nephew is a big Jason Aldean fan, and the fact that he wasn't there ... it's so hard to think about, if he was there what he would've seen, and just getting him out of there would have been horrific in every sense of the word."
Derby thought he heard fireworks, but as Aldean sprinted off the stage, he realized it was gunfire. Amid the mass confusion, he found his cousin and aunt, and ran for cover.
"At that point, we didn't know where the shots were coming from," he said. "It sounded like it was on top of us. We had a sinking feeling that maybe he's shooting an automatic weapon from the top of the Mandalay Bay. It's kind of what everyone was thinking. Everybody got down, and we tried to get as low to the ground as possible. ... I turned around to find my aunt, and I'll never forget her face. We made eye contact, and it was that look like 'Are we about to die?' You could hear the bullets hitting, ricocheting, and it's kind of one of those moments where you don't know what to do, but you try to get out of there."
His group found cover in a "House of Blues" tent and spent what he estimated was 20-30 minutes trying to distance themselves from the gunshots. Derby helped cover and guide two girls near him, who were visibly shaken, to safety and they finally made it to the Tropicana.
"There were these women who were sitting there literally frozen in fear," Derby said. "We started picking people up and shoveling them to the [exit] toward the back, and we all went that way."
Derby eventually met up with his sister and brother-in-law in the lobby of the hotel, where they were helping those in need of medical assistance. It was, for Derby, just one of many episodes of heroism he witnessed, a point of solace in an unimaginably horrific day.
"There's a ton of people lying on the ground crying, scared," Derby said. "There was a corner that they designated for the wounded. My brother-in-law is a firefighter and used to be an EMT, and you see these people, and they ran over and immediately started helping without hesitating. They're grabbing gloves, they're grabbing gauze, bottles of water, they're helping these victims who are facing injuries that they never thought they'd face in their lives, and they're scared. They don't know where their family is. Especially running out of the venue, you see these victims carrying wounded people. It was incredible to see all these people helping each other.
"It was amazing and warming to see these people stay in harm's way to help other people who seemed helpless. They sat there crumpled with fear, and these people went out of their way, into the eye of the danger, to help. That was incredible. At a time like this, it was refreshing to see in such a negative, negative day."
Derby remains in Las Vegas, because he is unable to get to his car, which is parked below the Mandalay Bay hotel where the shooter was located.
"I was actually staying at the Mandalay Bay on the 28th floor, so [four] floors under where the shooter was," Derby said. "My truck and my sister's car are in valet. We valeted the cars when we got here and apparently the shooter did the same, so they have that entire valet lot locked down. It's currently being investigated by the FBI."
For his part, Derby is still processing his experience, and what likely will be the permanent impact of that horror, and the sorrow and realization of his extraordinary luck in the face of hundreds of heartbreaking tragedies.
"To be honest, it hasn't even been 24 hours, so I've kind of been walking around today in a haze," Derby said. "It's weird to be walking around Vegas. ... There are people that were involved or even just were around the area at the time, and you can tell because they have a certain look on their face. Everyone's walking around like they saw a ghost.
"For me personally, processing this information is going to take a while. It's kind of one of those things where you always say that you never imagine yourself being in that position where you're running for your life and you're trying to make sure you have your loved ones by you. Because when there's thousands of people sprinting out at the same time all trying to survive, it gets dangerous. And I'm not talking about the shooting, I'm talking about stampeding and people trampling over each other. That's where it gets scary and deadly as well.
"Processing it is definitely going to take a little time on my end. I think it's definitely one of those things where you have to accept what happens and try to move on from it."