Balham
S24SU Seer
It's the amount of goals we would have expected to concede, based on the quality and frequency of chances that our opponents have had. In essence, we rarely allow our opponents to create high-percentage scoring chances. As the graph shows, we're better at that than any other team in the league, as of 34 games played.
As you point out, we've actually been pretty unlucky in that regard in conceding 40 when we've "deserved" to concede only ~28. The amount of long-range shots we've conceded from this season is genuinely freakish based on how often you'd expect shots from that range to hit the back of our net.
Edit - this is a good primer on expected goals, if you're interestedhttps://experimental361.com/explanations/match-timelines/
I genuinely can't remember a season where I've seen so many long range/phenomenal efforts go in against us. Certainly not since the days of Mark Bunn.
Off the top of my head I can think of 11:
Mendez-Liang, Cardiff (L0-2)
Phillips, Leeds (W2-1)
Grosicki, Hull (W4-1)
Palmer, Burton (W3-1)
Sessegnon, Fulham (L4-5)
Ojo, Fulham (L4-5)
Boga, Birmingham (D1-1)
Paterson, Bristol C (L1-2)
Snodgrass, Aston Villa (L0-1)
Neves, Wolves (L0-3)
Freeman, QPR (W2-1)
and that doesn't include Diogo Jota's team effort for Wolves.