It’s very legal! BB, Amex Specialists, Nasdaq MMs and NYSE Specialists gap up/down stocks up as you say. Just my experience watching for decades. Knowing this now, how will you use it to your advantage? There’s a reason why.
Algos, they pulled the same on Google. I just shut the computer off when my buy order on CGC was filled at $14.20. Sold $15.40 quickly, algos play games AH. You know from Cocoa Futures.