Nagal ran into a controversy when he was dropped from Davis Cup team for serious disciplinary issues. At Bengaluru Challenger Nagal stunned top seed Blaz Kavcic in quarter finals, followed it by beating compatriot Yuki Bhambri in semis and finally Jay Clarke in the Finals capturing his first challenger title.
Year 2019 proved to be breakthrough year for Nagal. At the 2019 US Open, Nagal qualified to make his grand slam main draw debut. He faced Roger Federer in his opening round match. He lost the match but managed to take first set against the multiple grand slam champion. Later he reached his second career ATP challenger final at the Banja Luka Challenger. He lost the championship match to dutch player Tallon Griekspoor. The next tournament he reached final again at Buenos Aires Challenger. He won the title defeating local player Facundo Bagnis. This was his second challenger title and first one on Clay.
In 2017, after reports came to surface that Sumit had missed a practice session in July 2016 at Chandigarh during the tie against South Korea, citing elbow injury. he was dropped from the Indian Davis Cup squad led by Anand Amritraj which was scheduled to face the New Zealand between 3 and 5 February 2017. A source close to All India Tennis Association told Sportskeeda, "It is a case of sheer indiscipline, on the part of the player. He missed several training sessions, brought his girlfriend to the camp without informing us. Several other discrepancies have also emerged, which led to the captain taking this call." Nagal denied the allegations, he got support from former India player Somdev Devvarman who stated that "I want to be clear once again. You have not chosen Sumit Nagal for the upcoming tie, because Sumit Nagal is NOT available to play. How do I know this? Because I have spent 2 weeks with Sumit in December helping him with his training and his rehab for the current shoulder injury he is recovering from."
Jay Clarke
Tallon Griekspoor
Facundo Bagnis