As a freshman at Connecticut in 2014, Kay appeared in 18 games and made eight starts. He went 5–4 with a 3.49 earned run average (ERA) and 56 strikeouts. As a sophomore, he started 14 out of 17 games and was 8–6 with a 2.07 ERA with 96 strikeouts.[2] As a junior, he started 17 games, going 9–2 with a 2.65 ERA and 111 strikeouts.[3] In 2014 and 2015, he played collegiate summer baseball with the Wareham Gatemen of the Cape Cod Baseball League.[4][5][6]
On July 28, 2019, the Mets traded Kay and Simeon Woods Richardson to the Blue Jays for Marcus Stroman and cash considerations.[11] Kay was added to the major league roster on September 7 to start against the Tampa Bay Rays.
With the 2020 Toronto Blue Jays, Kay appeared in 13 games, compiling a 2-0 record with 5.14 ERA and 22 strikeouts in 21 innings pitched.[12] In 2021, Kay made 11 appearances for the Blue Jays, recording a 5.61 ERA with 39 strikeouts across 33+2⁄3 innings of work.[13]
Kay dealt with an unspecified injury for most of 2022 and only made one appearance for the big-league club, in which he allowed one run in two innings of work. On December 16, 2022, Kay was designated for assignment following the signing of Chris Bassitt.[14]
Chicago Cubs
On December 23, 2022, Kay was claimed off waivers by the Chicago Cubs.[15] The Cubs designated him for assignment on January 20, 2023, after the signing of Trey Mancini was made official.[16] On January 24, Kay cleared waivers and was sent outright to the Triple-A Iowa Cubs.[17] In 23 appearances for Iowa, he registered a 4.50 ERA with 32 strikeouts in 28.0 innings of work. On June 13, Kay had his contract selected to the major league roster.[18] In 13 appearances for Chicago, he posted a 6.35 ERA with 8 strikeouts in 11+1⁄3 innings pitched. On September 11, Kay was designated for assignment following the promotion of Pete Crow-Armstrong.[19]
New York Mets (second stint)
On September 14, 2023, Kay was claimed off waivers by the New York Mets.[20] He spent most of his stint with the Triple–A Syracuse Mets; in four appearances for New York, he struggled to a 7.36 ERA with three strikeouts in 3+2⁄3 innings of work. Following the season on October 20, Kay was removed from the 40–man roster and placed on outright waivers.[21]
On October 24, 2023, Kay was claimed off waivers by the Oakland Athletics.[22] On November 6, Kay was removed from the 40–man roster and sent outright to the Triple–A Las Vegas Aviators.[23] He elected free agency the same day.[24]