- Bats Right, Throws Right
- Height 5' 9"
Holmberg hit .300/.611/.300 for Sweden with 7 runs in 5 games in the 2012 European Junior Championship Qualifiers, starting at catcher. He was 5th in the event in OBP and tied for 5th in runs.  He debuted in Sweden's Elitserien in 2013, hitting .269/.406/.269 in limited time for Akademin, while opponents stole 14 bases in 14 tries.  In the '13 European Junior Championship, he produced at a .261/.292/.348 clip but score six times in five games to tie Emil Sahlin for the team lead. 
He batted .416/.487/.416 for Akademin in 2014, but did not play enough to qualify for the batting leaders. It did win him a spot on the Sweden team for the 2014 European Championship. Only Arvid Carlstedt was younger on the squad; Holmberg saw a fair bit of action backing up veteran Björn Johannessen at catcher. He replaced Johanessen in the 4th inning against Italy with Sweden already out of the game. He was retired by Yomel Rivera his first time up but later singled off Nicholas Morreale and scored on a homer by Simon Emanuelsson. He later added a two-run double against Germany's Wolfgang Reitter and a two-run single against Croatia's Matko Dabo to finish the Euros at .300/.300/.400; his 4 RBI tied Philip Gajzler for second on the team despite his backup role. 
For Akademin in '15, his batting line was .295/.403/.318. In the 2015 B-Level European Championship, he hit .188/.278/.255 as a semi-regular for Sweden (3 starts in 5 games) as Sweden retained their spot in Europe's top competition. 
Like some other Swedish players, he came to the US for college but was redshirted in 2016.  He also played that summer for the Stockholm Monarchs, batting .194/.325/.194. He fell to .160/.250/.160 for Stockholm in 2017, splitting time with the even-younger Max Hill. At American River College in 2017-2018, he was 2 for 9 with two walks. 
Holmberg eked out just a .132/.233/.161 batting line for the 2018 Monarchs but fielded .990, 3rd among Elitserien backstops behind Mikael Lindqvist and Kestas Vilimas. His 16.6% caught stealing rate, unimpressive by US standards, was also good for 3rd. His average, though, was second-lowest among qualifiers, as were his OBP and slugging. He was still only 22 but his production was heading in the wrong direction.