Hail to the Chief!
I know what you are all asking: "BlueEyedRook, please provide us the Class-E analysis that only your "special" chess-playing background can provide." Your wish is my command . . . . let's look at one of the key moves of the game.
Costigan's opponent has just played 30. Nd4 in what has – up to now – been a pretty even game. Unfortunately, this proves to be a costly mistake. Richardson, again, demonstrates his ruthlessness at exploiting the slightest of errors.
30 . . . Nxf3+ (see below) is decisive.
White must clearly retake the knight, but neither of his three options are favorable.
Option 1 -- 31. Qxf3 is the biggest of the losing moves as black can simply pile his pieces on the lower right hand side of the board (see diagram below showing how easy black's pieces, highlighted in red, can wreak havoc on white's kingside). This proves for some downright devastating continuations all starting with 31… Bxd4+.
Option 2 -- 31. gxf3 is better, but still a clear loser. 31… Bxd4+ not only regains the sacrificed knight at the expense of a white pawn, but it leaves white with not two, not three, but four isolated pawns. Add to this the gaping hole in front of white’s king, and this spells a clear advantage for black (see diagram below).
Option 3 -- 31. Nxf3, the move actually chosen, eliminates the 31. . . Bxd4+ option that plagued the other two contenders, but white’s position is no less better as black now has three of his pieces (highlighted in red in diagram below) looming down on the knight – which is only guarded by two pieces. 31. . . Rxd4 is inevitable and again white finds itself a pawn short and with a whole heck of a bunch of trouble staring down the kingside.
Costigan went on to decively win the game.
From a club-level perspective, I like to see moves like this. Each of the continuations after 30. Nd4 is simple to see and realize on its own, but it is Costigan's ability to recognize all three variations (and quickly -- that chess clock never stops ticking) that separates him from the rest of us -- mere mortals! Nice game!
Congratz to the Philly team on their fine win!