William Morrissey was born in the Glendale neighborhood of New York City’s Queens borough on August 16, 1986. He is of Irish and Italian descent. He attended Archbishop Molloy High School and served as a peer tutor, homeless shelter volunteer, and National Honor Society member. He played basketball in his senior year and was featured in the Catholic High School Athletic Association Senior Classic All-Star game. After graduating from high school, he received a scholarship to attend New York University (NYU). He entered the pre-medical track before shifting to economics. While attending NYU, he played as a center for the NYU Violets from the 2005–2006 and 2008–2009 seasons. He co-captained the team for his final season. After graduating from NYU, Morrissey founded a ticket brokerage specializing in events held at Madison Square Garden and Yankee Stadium.

Morrissey trained as a professional wrestler at Johnny Rodz’s wrestling school in Brooklyn, New York. He debuted in Rodz’s World of Unpredictable Wrestling (WUW) promotion on May 30, 2009 under the ring name Big Bill Young with the gimmick of a cowboy, accompanying his storyline uncle Billy Walker to the ring. His first match in WUW and in his career as a whole was on August 15, 2009, and he went on to wrestle a number of matches for the promotion before signing with WWE in mid-2011.

In June 2011, Morrissey signed with Florida Championship Wrestling (FCW), which was WWE’s developmental territory at the time. Morrissey made his first televised FCW appearance in July 2011, portraying the dean of the University of Florida. Morrissey wrestled his first televised match under the ring name of Colin Cassady on the September 4, 2011 episode of FCW TV in a disqualification loss to Richie Steamboat. Cassady found no immediate success, losing matches for the rest of 2011 and in early 2012. Cassady scored his first win on the March 11 episode of FCW TV, defeating Kenneth Cameron. Cassady’s final FCW TV match was on July 7 in a win against Aiden English. WWE rebranded its developmental territory, FCW, into NXT in August 2012.

Cassady debuted on NXT television on June 5, 2013 with a loss to Mason Ryan. Cassady then formed a tag team with Enzo Amore, who had also previously lost to Ryan, and they labelled themselves “the realest guys in the room”. In real life, Cassady first met Amore at the age of 15, when they played basketball together at West Fourth Street Courts in Manhattan, New York. Ryan defeated Amore and Cassady in consecutive singles matches, but lost to them in a handicap match. Ryan ultimately had the last laugh when he caused Amore and Cassady to be attacked by Tons of Funk (Brodus Clay and Tensai). Amore and Cassady then feuded with Sylvester Lefort and his stable of Alexander Rusev and Scott Dawson. On the September 25 episode of NXT, Amore and Cassady participated in a gauntlet match for a future title shot at the NXT Tag Team Championship; they started the match and defeated Tyler Breeze and CJ Parker, then beat Rusev and Dawson, before falling to their final opponents, The Ascension (Conor O’Brian and Rick Victor). Amore suffered a legit broken leg in November 2013, which led Cassady to try his hand at singles competition, feuding with Aiden English. Amore returned on the June 26, 2014 episode of NXT, saving Cassady from an attack from Sylvester Lefort and Marcus Louis.

Morrissey met his future tag team partner Eric Arndt (Enzo Amore) when they played basketball together at the Cage in Manhattan, New York, nearly 10 years before they reunited in WWE in August 2013. Their 15-year friendship ended after Morrissey suffered a legitimate knee injury and Arndt was publicly critical of him for not finishing their match after the injury. The two have since reconciled.

Amore and Cassady proceeded to form an alliance with the debuting Carmella after the duo had accidentally cost Carmella her hairdressing job as per the storyline, causing her to demand to get a job as a wrestler. Carmella had her televised in-ring debut on the October 16 episode of NXT. In March 2015, Amore and Cassady began a rivalry with then NXT Tag Team Champions Blake and Murphy, with the champions insulting Amore and Cassady while attempting to woo Carmella. Amore and Cassady defeated The Lucha Dragons (Kalisto and Sin Cara) in a number one contender’s match for a title opportunity against Blake and Murphy. Amore and Cassady received their title match at NXT TakeOver: Unstoppable, but they lost after Alexa Bliss interfered. At NXT TakeOver: London, Amore and Cassady challenged Dash and Dawson for the NXT Tag Team Championship in a losing effort. They were granted another title opportunity against Dash and Dawson in March 2016 at Roadblock, which Amore and Cassady lost.

On the Raw after WrestleMania 32, Amore and Cassady made their main roster debuts and confronted The Dudley Boyz. On the April 14 episode of SmackDown, Amore and Cassady defeated The Ascension in their main roster debut match, advancing in the WWE Tag Team Championship number one contenders tournament. In the finals, Amore and Cassady faced The Vaudevillains at Payback, with the match ending in a no contest after Amore suffered a legitimate concussion during the match. In May 2016, Cassady’s ring name was changed to Big Cass. On the June 6 episode of Raw, during the match between Enzo and Cass and The Vaudevillains, Cass witnessed English attempting to injure Enzo in a similar manner of what Gotch did to him at Payback. This led to Cass attacking The Vaudevillains, including executing an East River Crossing on Gotch. At Money in the Bank, Enzo and Cass competed in a fatal four-way tag team match also involving The New Day, Luke Gallows and Karl Anderson and The Vaudevillains for the WWE Tag Team Championship, which they lost. On the July 4 episode of Raw, Enzo and Cass helped John Cena from an attack by The Club, involving themselves in the feud between Cena and The Club. At Battleground, Enzo and Cass teamed with Cena to defeat The Club in a six-man tag team match.

At the 2016 WWE draft on July 19, Enzo and Cass were drafted to Raw. Following Battleground, Enzo and Cass feuded with Chris Jericho and Kevin Owens, losing to them at SummerSlam. On the August 22 episode of Raw, Cass defeated United States Champion Rusev by countout to qualify for the fourway elimination match for the WWE Universal Championship. In that match, the biggest of his career, which also included Kevin Owens, Roman Reigns and Seth Rollins, Cass was eliminated by Owens, marking the first time he was pinned on the main roster.

Cass returned during the 2018 Superstar Shake-up, which moved him to SmackDown. On the April 17, 2018 episode of SmackDown, he interrupted the main event and attacked Daniel Bryan. The following week on SmackDown, Cass would take Bryan’s spot as the guest on Miz TV, where it would be later revealed that Cass had attacked Bryan backstage. At Greatest Royal Rumble, Cass would enter the 50-man Royal Rumble match at number 49, where he would eliminate Bryan, lasting until the final two before being eliminated by Braun Strowman. At the Backlash pay-per-view, Cass was defeated by Bryan after submitting to the Yes Lock, only for Cass to attack Bryan after the match. On the May 29 episode of SmackDown, he would unsuccessfully wrestle against Bryan and Samoa Joe in a triple threat Money in the Bank qualifying match after Joe applied the Coquina Clutch on Bryan. At Money in the Bank, Cass lost to Bryan again in a singles match via submission. This would be his last match with the WWE, as he was released on June 19, 2018. According to Sports Illustrated, Morrissey’s release was due to behavioral issues including public intoxication during a WWE tour and disobeying direct orders from Vince McMahon, in particular relating to an on-air incident involving an attack on a little person who was impersonating Daniel Bryan on the May 1 episode of SmackDown.

On December 8, 2018, Morrissey suffered an epileptic seizure while at his merchandise table during a House of Hardcore event. He was treated by medical personnel while Tommy Dreamer and Bubba Ray Dudley were by his side. He was responsive and eventually taken to the hospital.

On April 6, 2019, Morrissey, alongside former tag partner Enzo Amore, appeared at the G1 Supercard at Madison Square Garden. Following a tag team match involving Ring of Honor and New Japan Pro-Wrestling talent, the two jumped the barricade and attacked several wrestlers. The broadcast cameras cut away from the incident to indicate a legitimate outside attack, but it was later reported the angle was a worked shoot. However, following the angle, the duo were not booked for any following shows and the incident was never mentioned again.

On June 15, 2019, Morrissey, under the ring name of CaZXL, made his debut for Northeast Wrestling (NEW), where he was accompanied by Arndt, now known as nZo. Caz then issued an open challenge to anyone on the roster. Jon Moxley would answer the challenge and later defeat him in a match.

On September 14, 2019, Morrissey was involved in an incident backstage at a WrestlePro independent show where he allegedly confronted and tried to fight Joey Janela (who was involved in an incident with Morrissey’s tag team partner, Eric Arndt, months earlier) and he also allegedly confronted and spat in the face of independent wrestler Pat Buck. According to witnesses, Buck retaliated by punching Morrissey in the face. Morrissey was kicked out of the building, and police officers were called after he refused to leave. No charges were filed.