Might be tempting fate here but Brentford don't really have a reputation for being rough or scrappy, which means the allowances Luton were afforded might not come into play here. Thought Luton were allowed to be aggressive and rough against City in a way that crossed a line but cos they were the underdogs in a scrappy little hostile stadium the refs just let yellow cards go cos "it's expected at a place like this". Not saying Luton were wrong to do what they did - they've got to level the playing field somehow - but refs weren't interested in getting wise to it cos of preconceptions about both sides. Whereas Brentford are an established side who play in a nice modern ground on a flat surface and those things do get taken into account by refs as to whether a booking is worth it. It's slightly easier to book a home player in a ground like Brentford's than Luton's. As evidenced by Luton being at the top of the Fair Play table and Brentford being just that bit further down: https://www.transfermarkt.co.uk/premier-league/fairnesstabelle/wettbewerb/GB1. Chelsea have the most yellow cards in the league this season and I reckon at least 15 of them have been given because certain tackles are deemed "out of character" by referees and therefore punished more severely.It's a small pitch here which never suits us. Luton was a good example of that although we navigated it well.