Satoshi was well aware of the Nailgun's maximum capabilities. He knew just how powerful every piece of nail it fired from its casket, how it could pierce through anything he willed it to. And well, Sai Tama wasn't exactly the opponent that Satoshi would hold back on. He was a formidable superhero, and this prompted Satoshi to attack him with full force.
Despite all that, the nails seemed to bounce off his skin. Satoshi's confidence dwindled. Because at that moment, he was fairly certain that he had caught Sai Tama off guard. In doing so, he left a lot of openings on himself that second when he counterattacked, and Sai Tama wholly took advantage of it.
"That was pretty good, Satoshi, but you have to do better than that if you want to defeat me." Sai Tama smiled to himself as he held Satoshi by the neck, raising him up.