It's actually the rule that leaves room for subjectivity. VAR is more or less clear. The problem is the interpretation. To say 'every attacker n the box is affecting play' as the pundit did is contrary to the rule.
I've always thought it was unfair that, had Ox then passed it to Firmino who subsequently scores, Firmino is deemed to be onside again. As 19x said, it's the phases of play aspect of the rule. In real time it's very confusing for defenders who have worked cleverly to make sure he was offside.
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