I take PoPs point about set pieces being generally a low-percentage situation, and acknowledge that his vast experience in coaching qualifies him to make such statements. But I do wonder if set piece scoring rate at the top professional level is different from that in the lower tiers. Seeing the fine lines which divide the top teams, it is not unimaginable that the best teams (especially professionals training full-time) spend slightly more time practicing attacking set pieces.
Anyway, according to
Whoscored.com, every team has played 18 matches. A total of 479 goals have been scored, of which 113 have come from set pieces, which means that
23.6% of all goals scored have come from set pieces (not including penalties and OGs which may have resulted indirectly from set pieces).
According to the OP, we've conceded 7 goals in the league from set pieces (again, minus penalties and OGs) out of 21 goals conceded,
a rate of 33.3%. So I think it's true that this season, we've conceded proportionately more goals from set pieces as compared to other teams.
If we look at it as set piece goals conceded per game,
we've conceded 7 in 18 games which is 0.389 per game. Across the league, 113 SPGs have been conceded over 360 games,
which is a rate of 0.314 per game. So we've been conceding set piece goals 24% faster than the league average.
Since we concede set piece goals faster than the league average, with a defence that has been conceding goals slower than the league average (average total goals conceded per team is 23.95, we're on 21), I daresay that we are below average at defending set pieces.Caveats:
A better comparison perhaps would be to count goals conceded from set pieces against total number of set pieces faced, but again, it's hard to find those numbers. This would probably be the best measure, but it'd be bloody difficult to count. I guess if we added all the corners a team gets, plus all the attacking-third free kicks, it would give an approximate number....
Again, there doesn't seem to be easily available statistics on how many goals each team concedes from set pieces, so it's not possible to tell how we compare against other individual teams, unless someone compiles data like the OP did.
Lastly, if anyone has suggestions on how to present the above information better, I'm open to hearing it.
Edit: bolded some stuff to try and highlight the important numbers