does the ball need to clear the yellow line or any part of the ball touches the yellow line would count as a HR?
Yellow line is in play (that's an MLB-wide ground rule). If it hits it and goes back on the field it's a live ball, if it hits it and bounces into the stands or then comes in contact with something above the yellow (like a railing or fence or whatever) then it's a HR.
Front row of Crawford Boxes, leaned over and interfered with Yordan's line drive that was about to bounce off the top of the wall, almost fell over the railing onto the field. Fan interference cost the Stros a run (they got it back on a Sac Fly later). According to Chandler Rome, he was escorted out of the stands by security.
MM rules: Left field RULE #8: Batted ball in flight strikes yellow line on fence or top of railing in left-center field at a point above the stands and bounds into stands: Home Run.
Just FYI: That particular rule pertains to the jag where the Crawford Boxes angle back to meet the LCF wall. https://www.mlb.com/groundrules/venue-2392