Kozina started his youth career in RK Matulji before establishing himself in Zamet the premier handball club of Rijeka.
After four seasons he moved to NEXE. While there he debuted in his first European competition EHF Cup. In 2013 he moved to AustrianAlpla HC Hard. With the club he started winning his first trophies as a club player.
In December 2016 Kozina was invited to national team training for the upcoming 2017 World Championship as a replacement for Marino Marić who was injured.[11]
Kozina appeared at the HEP Croatia Cup in their match against Tunisia and scored two goals before being gaining 2 minutes at the end of the match.[12] He didn't appear in the match against Montenegro. Croatia won the HEP Croatia Cup.[13]
On 10 January Željko Babić announced the players he would be taking to France, Kozina was not on the list.[14]
Personal life
Kozina has a younger brother Bruno who is also a handball player.[15]