In a 107–66 blowout win against the Washington Huskies, Ball had 22 points, six rebounds, and five assists. With close to two dozen NBA executives in attendance, the game matched Ball against the Huskies' Markelle Fultz, who were among the nation's top point guards and projected to be among the top picks in the 2017 NBA draft. Fultz scored 25 points in an even matchup between the two freshmen. In the Bruins' regular season finale, Ball had a career-high 14 assists in a 77–68 win over Washington State, when he also broke Gary Payton's 30-year-old Pac-12 season record for assists by a freshman. UCLA was seeded No. 3 in the NCAA Tournament, and won their opening game 97–80 over Kent State. Ball had 15 points and three assists to surpass Larry Drew II's school record for most assists in a season. In the second round, he flirted with a triple-double with 18 points, seven rebounds, and nine assists in a 79–67 win over Cincinnati. All of his assists came in the second half, when UCLA overcame a three-point halftime deficit after scoring a season-low 30 points in the first half. The Bruins were eliminated in the Sweet 16, losing 86–75 to Kentucky. Ball had 10 points, eight assists, and four turnovers in the loss, while Wildcats point guard De'Aaron Fox scored 39 points for an NCAA tournament freshman record. Ball strained his hamstring in the game and was limping in the second half, but did not offer it as an excuse for being outplayed. After the game, he announced that he would declare for the 2017 NBA draft, where he was generally projected to be a top-3 pick.
As a rookie in 2017–18, Ball played in 52 games, missing 30 games due to shoulder and knee injuries. In the second game of the season on October 20, 2017, he scored a career-high 29 points, to go along with 11 rebounds and 9 assists in a 132–130 win against the Phoenix Suns, falling one assist shy of becoming the youngest player to notch a triple double in NBA history. In the following contest, he had eight points, eight rebounds, and 13 assists in a 119–112 loss to the New Orleans Pelicans, becoming the youngest player in franchise history to get at least 10 assists in a game. On November 11, he recorded 19 points, 13 assists, and 12 rebounds in a 98–90 loss against the Milwaukee Bucks, becoming the youngest player at the time to achieve a triple-double at the age of 20 years and 15 days old, breaking James's record by five days. Leading up to the game, Bucks' coach Jason Kidd, who Ball is often compared to, had called it "a stretch" to compare the two since it was too early in Ball's career. Ball, who had been struggling with his shooting, made over 50% of his field goals in a game for the first time in his career. On November 19, he recorded his second triple-double with 11 points, 16 rebounds, and 11 assists in a 127–109 win over the Denver Nuggets. It was the most rebounds by an NBA rookie guard since Steve Francis had 17 in 1999–2000. He also joined fellow NBA rookie Ben Simmons, as well as Magic Johnson, Connie Hawkins, Art Williams, and Oscar Robertson as the only players to record multiple triple-doubles within the first 20 games of their NBA careers.
Ball began his pro career using sports apparel from his father LaVar's Big Baller Brand instead of signing with any of the major apparel companies. His father had insisted that he not sign with a company unless they agreed to license merchandise from Big Baller Brand. In May 2017, Big Baller Brand announced the release of Ball's first shoe, the ZO2. The $495 price tag on the shoe sparked wide criticism from celebrities and on social media. In response to his critics, LaVar tweeted on May 4, "If you can't afford the ZO2S, you're NOT a BIG BALLER!" It was later revealed that despite not being a founder of the company, Lonzo owned 51% of the Big Baller Brand, while his father owned 16.4% of the business and both his mother and Alan Foster owned 16.3% of the business. On April 6, 2018, Jordan Crawford became the first player besides Ball to wear the ZO2s during a game.
On December 20, 2017, Ball was announced as the logo for the Junior Basketball Association (JBA), a league his father LaVar planned to establish for high-school basketball players who have finished high school but want an alternative option to the NCAA.
In September 2017, Ball released his first rap single, "Melo Ball 1", an ode to his youngest brother, LaMelo. Not long after, during that same month, he released the song "ZO2", a dedication to his own brand of shoes. It would later be his lead single for his upcoming debut album. The following month, Ball released another rap single titled "Super Saiyan", which is a nod to the anime and manga series Dragon Ball Z. In the track, he compares himself to Goku, the main protagonist of DBZ. On February 15, 2018, Ball and his father would participate in the Lip Sync Battle as competitors. That same day, Ball released his debut album, Born 2 Ball, under the name Zo. The album would be released under the Big Baller Music Group, a subsidiary of the Big Baller Brand, run by a close friend of his father. In March, Born 2 Ball peaked at No. 42 on Billboard's Independent Albums chart and No. 13 on its Heatseekers Albums chart.
In February 2017, Ball's mother Tina suffered a stroke and was hospitalized for two months.
Ball is a rap music enthusiast; in his spare time he writes lyrics on his phone, He also frequently goes to a studio to record music. He has said that he would be a rapper if he was not an NBA player. In August 2017, Ball and his family premiered in their Facebook Watch reality show, Ball in the Family.