Man City was denied a penalty by VAR in Southampton’s 5-2 win.
Phil Foden was taken down by Saints goalkeeper Alex McCarthy and VAR decided not to award a penalty.
City later extended their lead to 14 points in the Premier League table, thanks to both Kevin De Bruyne and Riyad Mahrez scoring a brace.
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“There are things that are hard to understand,” said Pep Guardiola, who also highlighted some other recent VAR controversies involving other clubs.
“So maybe one day they can explain the rules about the VAR. Hopefully one day they can explain what is going on.
“Jon, the referee, OK he cannot see it, the linesman cannot see it, (but if) the VAR cannot see it – Oh my God.
“You just want it to be more clear, and the right decisions. We won 5-2 but if we’d lost 5-2 I don’t make any comment. After you win you can do it, if not it looks like an excuse.”