One Punch Man's bald hero Saitama smashes monsters with effortless strikes, but his perfect combat history hides an awkward truth. The clearly invincible protagonist has actually tasted defeat a considerable times throughout the series, though never in the way most people would expect.
Saitama's failures don't come from epic baddie showdowns or catastrophic fights that shake the earth. Rather, his defeats originate from ordinary cases like childhood bullying, video game competitions, and his endless struggle against a single mosquito that refuses to die. These odd failures expose the ironic constraints of unlimited power in One Punch Man.

During his middle school years, Saitama faced his first significant defeat. Two third-year students faced him in an alley, ordering his wallet. Even though Saitama tried to resist, he didn’t have the strength to stand against the two bullies. They quickly overpowered him and took his 200 yen, giving him his first real taste of defeat in One Punch Man.
Right after Saitama’s run-in with the bullies, a strange creature named Piggy Bancon robbed the very same students who had just taken his money. When he heard a bully remark needing the money for his younger brother's lunch, Saitama's sense of justice kicked in. He charged at the monster to retrieve the stolen funds. However, Piggy Bancon easily defeated him, crashing him into a wall and leaving him out cold for over an hour.
Gaming Defeats and Strategic Defeats in One Punch Man

Perhaps Saitama's most regular losses in One Punch Man occur during video game sessions with King. The S-Class hero holds an undefeated streak against Saitama, beating him 81 consecutive times in different gaming contests. King's gaming prowess is so superior that he can beat Saitama even while handicapped with one arm tied behind his back.
These gaming defeats highlight an interesting aspect of Saitama's character. Despite possessing unlimited physical power, he struggles with activities requiring specific skills outside of combat. His frustration with these losses shows that even the strongest hero in the series has areas where he cannot dominate.
Silver Fang, also known as Bang, has invariably beaten Saitama in classic games. Their matches of Rock, Paper, Scissors have resulted in multiple victories for the elderly martial arts master. These defeats explain that raw power cannot overcome strategy, luck, or experience in certain contexts within the One Punch Man universe.
The Infamous Mosquito Battle

One of the most memorable non-combat defeats in One Punch Man applies to a simple mosquito. Despite his outstanding speed and precision in battle, Saitama cannot successfully eliminate this tiny insect. The mosquito unfailingly evades his attempts at destruction, creating comedic moments that subvert expectations about his abilities.
This ongoing loss denotes, maybe, the most ironic defeat in the series. A hero capable of destroying planets struggles against one of nature's smallest creatures. The mosquito performs as a running gag that underscores the absurd nature of Saitama's circumstances.
Saitama's defeats help important narrative objectives within the series. They humanize a character who might otherwise seem too flawless or detached from normal experiences. His efforts with everyday activities form relatable moments for audiences.
While Saitama is still unbeaten in real combat within One Punch Man, his mixed defeats in other areas make him a more complete and fascinating character. All these failures provide compulsory character moments and comedic comfort.