Warning: the following article contains spoilers for Jujutsu Kaisen Chapter 170 "Tokyo No. 1 Colony, Part 10," by Gege Akutami, John Werry, and Snir Aharon, available in English from Viz Media.
Fushiguro was oozing confidence in his ability to take on Reggie at the end of the previous chapter. He essentially told Reggie to be worried because he'll be able to fight for real now. He was facing multiple enemies on his own before Takaba Fumihiko showed up so he wasn't able to fight earnestly. Now that it's just Fushiguro and Reggie, the first-year is ready to go all out.
Fushiguro's confidence was misplaced, as it turns out. Reggie had been on the sidelines up to this point, allowing his allies to fight Fushiguro and keeping his Cursed Technique a mystery. In other words, Fushiguro had no idea what Reggie was capable of until the two started fighting. Reggie finally revealed his Cursed Technique in Chapter 170 and it's quite troublesome.
Reggie's Cursed Technique is called Contractual Re-creation. It allows him to re-create contracts and manifest objects from them. That included the receipts he's currently wearing on his body. The way it worked was interesting because objects aren't the only things he could manifest from the contracts. He demonstrated this to Fushiguro by using a receipt for a three days and two nights stay at a five-star inn, complete with an oil treatment. He was suddenly cleaned, healed, and rested as if he actually relaxed for two days at a hot spring.
The things Reggie recreates with his contracts act like shikigami. In other words, he can command inanimate objects to do as he pleases. This is trouble for Fushiguro and he quickly realized that. Reggie's body is covered in receipts so he likely has more he can use to heal himself. Fushiguro was already so exhausted from all the fighting he's done that he's unable to summon his Divine Dog shikigami. Reggie let him know he's aware of this, leaving Fushiguro no choice but to run away.
Fushiguro ran but Reggie had no problem keeping up with him or keeping track of where he's going. He simply used his technique to conjure a scooter and some drones. Reggie wondered if Fushiguro was simply running or luring him in when he gets to his location. It turned out that he was in fact luring him into a gymnasium. Reggie considered forcing him out with fire but opted not to because he'd rather not chase him again.
Reggie entered the gymnasium and ruthlessly beat on Fushiguro by summoning multiple different objects including whole trucks and knives. Fushiguro was so busy trying (and mostly failing) to avoid these attacks from conjured objects that it was even harder for him to think about avoiding Reggie's own physical attacks. When it seems like Fushiguro is done for, he does what he lured Reggie into the gymnasium. He used his Domain Expansion, Chimera Shadow Garden.
Reggie is shocked by this as he had no idea this teenager was a sorcerer of this level. He assumed that Fushiguro didn't have any big moves and his decision to not force him out of the gymnasium with fire may prove to be fatal mistakes. However, Fushiguro's Domain is still incomplete since he hasn't perfected his technique. That's the entire reason he lured him to the gymnasium in the first place. Reggie may be able to overcome this somehow, in which case Fushiguro would be defeated since using his Domain Expansion at this point will most likely drain his last bit of energy.