Hamer began his collegiate career at Division II College of St. Rose where he spent the 2021 and 2022 seasons. He played in a total of 23 games at St. Rose, making 17 starts, while holding a .237 batting average with one homer and eight RBI. He spent the 2022 summer playing for the Oneonta Outlaws of the New England Collegiate Baseball League where he bat .261 in 27 games with two home runs and 21 RBI. Hamer then transferred to Division III SUNY Oswego where he found his stride. He bat .315 in 2023 while hitting five home runs, knocking eight doubles, and snatching 29 RBI earning a spot on the 2023 SUNYAC All-Conference First Team. He exploded in 2024 as he held a batting average of .437 while smacking 21 doubles, launching 7 bombs, and bringing in 39 RBI. He was named the SUNYAC Bob Wallace Player of the Year, D3Baseball.com Region 3 Player of the Year, and ABCA/Rawlings Second Team All-American.