2014-19

On September 19, 2014, at the age of 20, Shmailov took part in the under 21 European championship which was held in Bucharest and won the gold medal after winning every match by ippon.^[19][20] About a month later, he participated in the 2014 World U21 Championships in Fort Lauderdale and won the bronze in the under 66 kg category after losing the semi-final match to Japan's Hifumi Abe and defeating Ukraine's Bogdan Iadov in the bronze medal match.^[21][22][23] On November 14, he won the 2014 European U23 Championships after defeating Andraž Jereb of Slovenia in the final.^[24][25]

On March 20, Shmailov won his first medal in a senior competition when he won a silver medal at the 2015 Tbilisi Grand Prix.^[26][27] He defeated former world champion Georgii Zantaraia in the semi-final and lost to Mongolia's Tumurkhuleg Davaadorj in the final. On October 7, he took part in Israel's national championship and won the gold medal after he defeated Tohar Butbul in the final.^[28]

In September 2016, Shmailov participated in the Zagreb Grand Prix and won the silver medal.^[29][30] On March 10, 2017, he won the bronze medal at the Baku Grand Slam^[31][32] after defeating Nijat Shikhalizada of Azerbaijan in the medal match. Less than a month later he won the bronze at the 2017 Antalya Grand Prix.^[33][34]

On December 16, 2017, Shmailov took part in the prestigious World Masters which was held in St. Petersburg and won the bronze medal^[10][11] after he defeated Brazil's Charles Chibana in the medal match. On February 23, 2018, he won a bronze medal at the Düsseldorf Grand Slam after defeating Russia's Yakub Shamilov in golden score of the medal match when he managed to get a pinning hold on his opponent.^[35][36]

Shmailov competed in the 2018 World Masters tournament and won the silver medal.^[12][13] In the quarter-finals he defeated then European champion Adrian Gomboc of Slovenia by ippon, in the semi-finals he defeated Daniel Cargnin of Brazil by ippon as well, and in the final lost to Joshiro Maruyama of Japan by ippon.

2020-present

In 2021, he won the silver medal in his event at the World Masters held in Doha, Qatar.^[37][38][39]

After a long contest with Tal Flicker, Shmailov was chosen to represent Israel at the 2020 Summer Olympics in the men's 66 kg weight category.
In his first match, Shmailov beat Mozambique's Kevin Loforte by ippon. At the round of 16, he beat Australian Nathan Katz by waza-ari, advancing to the quarterfinals. There, he met former European champion Vazha Margvelashvili of Georgia, losing by ippon and turning to compete at the repechage for a chance to win a bronze medal. In his next match, Shmailov beat Slovenia's former European champion Adrian Gomboc, beating him by waza-ari in golden score and advancing to fight for the bronze. Shmailov lost the bronze medal match to Brazilian two-time Pan American champion Daniel Cargnin, finishing in fifth place.^{[14][15][16][17]}

He won the gold medal in his event at the 2022 Judo Grand Slam Tel Aviv held in Tel Aviv, Israel.^[40]