Freshman In November 2013, Welsh committed to play at UCLA over fellow Pac-12 schools
California and
Stanford. As a freshman with the Bruins in
2014–15, he spent most of the season as a backup to junior
Tony Parker. Welsh played in all 36 games, starting in three, and averaged 3.8
points and 3.8
rebounds per game. He led the team in
blocks, averaging 1.1 per game as a reserve. He became the Bruins' first 7-foot player since
Ryan Hollins in
2005–06. In the season opener against
Montana State, Welsh scored 14 points in 13 minutes of play. He had six rebounds and four blocked shots in 22 minutes in an upset victory over
SMU in UCLA's opening game of the
2015 NCAA tournament. Playing the final minutes of the game in place of Parker, he made a key block with 34 seconds remaining and UCLA down by four.
Sophomore Having
played on the U.S. under-19 national team over the summer, Welsh's footwork and fundamentals improved. With
Kevon Looney having moved on to the
National Basketball Association (NBA), Welsh was promoted to UCLA's starting lineup at center, while Parker moved to
forward. In the
2015–16 season opener, he had his first collegiate
double-double with 12 points, 10 rebounds and a career-high five blocks in an 84–81 overtime loss to
Monmouth. The blocks were the most by a Bruin since
Travis Wear's five in 2012. In the following game, Welsh scored a career-high 22 on 10-for-12 shooting in an 88–83 win over
Cal Poly. On December 3, against No. 1
Kentucky, he registered game highs of 21 points and 11 rebounds and outplayed highly touted Wildcats freshman
Skal Labissière in an 87–77 upset win, the Bruins' first victory over a No. 1-ranked team since
2003. On January 9, 2016, he had a season-high 16 rebounds in an 81–74 win over
Arizona State, which helped UCLA avoid falling to 1–3 in the Pac-12 for the first time in almost 20 years. After UCLA lost three of four games in mid-February, Welsh became a reserve after offering to coaches that Parker could take his place in the starting lineup; the senior Parker had been benched in favor of a quicker
Jonah Bolden. The Bruins lost their final five games to finish with a 15–17 record. Welsh ended the season with an 11.2 scoring average, and led UCLA in
field goal percentage (59.0), rebounding (8.5) and blocked shots (1.0). He ranked seventh in the Pac-12 in rebounding, second in offensive rebounds per game (3.2), and third in field goal percentage. Welsh was leading the Bruins in rebounding again, but had missed the last four games with a bruised right knee. He returned in the conference opener, but the Bruins suffered their first defeat in an 89–87 loss to No. 21
Oregon despite Welsh's 20 points, 10 rebounds and three blocks. On February 19, 2017, he scored 16 points and had a season-high 16 rebounds in a 102–70 win over
their crosstown rivals,
USC, ending a four-game losing streak against the Trojans. On February 25, Welsh scored 12 of his 14 points in the second half to lead No. 5 UCLA to a 77–72 win over No. 4
Arizona, which also snapped
their conference rivals' 21-game home winning streak. In the Bruins' regular-season finale, he had 13 points and 11 rebounds and also made his first career
three-point field goal in a 77–68 win over
Washington State. The Bruins ended the season 31–5 after losing in the Sweet 16 of the
2017 NCAA tournament to Kentucky. For the season, Welsh averaged 10.8 points along with team highs of 8.7 rebounds and 1.3 blocks per game, and he received an honorable mention for the
All-Pac-12 team. Although he was not listed in most
mock drafts, he declared for the
2017 NBA draft. After attending the
NBA Draft Combine but not hiring an agent, he withdrew his name from the draft to retain his college eligibility.
Senior Over the summer, Welsh worked on his three-point shooting based on feedback from his NBA workout with the
Oklahoma City Thunder. He was the Bruins' lone returning starter in
2017–18. On December 9, 2017, he tied a career high with 22 points and added 10 rebounds in a 78–69 overtime loss to
Michigan. On January 4, 2018, Welsh required three stitches after being bloodied by a hit to his nose. He was forced him to wear a protective mask after halftime, which affected his shooting as UCLA lost 107–99 in double overtime. He continued wearing a mask the following game, but adjusted for 19 points, 14 rebounds, and a career-high four three-pointers in a 107–84 win over Cal. On February 15, he played his first game without a mask since January and logged a career-high 17 rebounds along with 15 points in a 75–68 victory over
Oregon State. In UCLA's
Pac-12 tournament opener, Welsh had 18 points, 11 rebounds, and tied his career-high of four three-pointers in an 88–77 win over Stanford. The Bruins qualified for the
2018 NCAA tournament, but lost 65–58 to
St. Bonaventure in the First Four for the Bonnies' first tournament win in 48 years. Welsh was limited to just two points, but had 15 rebounds to pass
David Greenwood as the Bruins' third all-time leading rebounder, behind only
Kareem Abdul-Jabbar and
Bill Walton. Welsh completed the season averaging 12.6 points and 10.8 rebounds. He made 40.2 percent (45-for-112) from 3-point range after attempting just one in his first three seasons. One of just two players along with Arizona's
Deandre Ayton to average a double-double in the Pac-12, he earned second-team
All-Pac-12 honors. The
United States Basketball Writers Association (USBWA) voted him to their All-District IX Team, and he was a finalist for the
Kareem Abdul-Jabbar Award, which recognizes the top center in
Division I men's college basketball. ==Professional career==