The highest 'single' score in darts is 60 (triple 20), in snooker is 7 (black ball) and in cricket is 7 (6 off a no-ball). If you argue the 147 is correct, then it too is incorrect: 155. To score 155, a foul stroke must be committed by an opponent, which leaves the non-offender snookered on all 15 reds. By nominating a colour as an ‘extra red’, then taking a subsequent black .... etc.

I doubt if anyone on this earth could figure group #4!

Apart from 'Numbers appearing in Sporting team names', and just maybe 'highest scoring in specific sports' (although that is stretching it a bit!)
The other two are not really connections, they are a collection of pub quiz trivia answers that have been lumped together.
For instance, why those particular sports for the team sizes, there is no link between them other than they are sports. You could say Lets put 6 in that category as the number of players in an ICE HOCKEY team, then place 5 in the scores row for the number of points for a try in rugby union. So you could also argue that there is not a unique solution also.
I also agree with what toeswest has stated regarding the scoring systems connection.
Apart from all of that......decent grid!