This is not unreasonably unfair to the teams in the pools of five. Presumably, the 17th and 18th seeds are in that pool which ought to be easy victories for any team that has a chance at finishing in the top two of the pool. There could be a problem, however, if not much is known about the teams, and the seeding is very inaccurate.
A possible nightmare occurs if there is a three-way tie for first, thus relegating a team with one loss to finish out of the top eight. This is a serious problem. This format was used at the 1989 South Fall Sectional in the Mid-Atlantic, and we simply crossed our fingers and hoped for the best. We were constrained by having only seven fields available, at three different locations. And we couldn't think of anything else that would fit. The three-way tie did not happen for us.
The schedules for five and four-game round-robins appear in Tables 5.1.1 and 4.1 respectively. You could simply give each pool two fields, and let them go at it. This would take up eight fields. A better schedule might be one below:
Fields: 1 2 3 4 5 6 7
9:00 D1-D3 D2-D4 C1-C4 A1-A3 A4-A5 B1-B3 B4-B5
10:45 D1-D2 C1-C3 C2-C4 A1-A5 A2-A4 B1-B5 B2-B4
12:30 D3-D4 C1-C2 C3-C4 A2-A5 A3-A4 B2-B5 B3-B4
2:15 D1-D4 D2-D3 C2-C3 A1-A4 A2-A3 B1-B4 B2-B3
4:45 A1-A2 A3-A5 B1-B2 B3-B5
Note that the round-robin for the two pools of four (pools C and D in this
example) are played over four rounds on three fields. They could be played
on three rounds on four fields, but there are two disadvantages of that
method. First, it takes up an extra field. Second, half of the teams
would be done after the third round while pools A and B still had two more
rounds to go. The schedule above uses less fields and keeps more players
around.
If you are simply running an 18-team tournament, without having to worry about teams qualifying to the next level, you have all kinds of flexibility. An easy format for the second day for the top two of each pool advance to a quarterfinal single-elimination, and the next two (third and fourth place teams) of each pool advance to a "Division II" quarterfinal single-elimination. (This 16-team Division I & II elimination is shown in Section 16.1.) Schedule the two remaining fifth place teams for a game on the second day, also.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
- - - - - - - - - -- -- -- -- -- -- -- --
1 - 17 4 9 14 18 6 11 16 3 8 13 5 10 15 2 7 12
2 - 16 3 8 13 5 10 15 18 7 12 17 4 9 14 1 6 11
3 - 15 2 7 12 17 4 9 14 1 6 11 16 18 8 13 5 10
4 - 14 1 6 11 16 3 8 13 5 10 15 2 7 12 17 18 9
5 - 13 18 10 15 2 7 12 17 4 9 14 1 6 11 16 3 8
6 - 12 17 4 9 14 1 18 11 16 3 8 13 5 10 15 2 7
7 - 11 16 3 8 13 5 10 15 2 18 12 17 4 9 14 1 6
8 - 10 15 2 7 12 17 4 9 14 1 6 11 16 3 18 13 5
9 - 18 14 1 6 11 16 3 8 13 5 10 15 2 7 12 17 4
10 - 8 13 5 18 15 2 7 12 17 4 9 14 1 6 11 16 3
11 - 7 12 17 4 9 14 1 6 18 16 3 8 13 5 10 15 2
12 - 6 11 16 3 8 13 5 10 15 2 7 18 17 4 9 14 1
13 - 5 10 15 2 7 12 17 4 9 14 1 6 11 16 3 8 18
14 - 4 9 18 1 6 11 16 3 8 13 5 10 15 2 7 12 17
15 - 3 8 13 5 10 18 2 7 12 17 4 9 14 1 6 11 16
16 - 2 7 12 17 4 9 14 1 6 11 18 3 8 13 5 10 15
17 - 1 6 11 16 3 8 13 5 10 15 2 7 12 18 4 9 14
18 - 9 5 14 10 1 15 6 2 11 7 16 12 3 17 8 4 13
1- 4 2- 3 5-18 6-17 7-16 8-15 9-14 10-13 11-12
1- 9 2- 8 3- 7 4- 6 5-10 11-17 12-16 13-15 14-18
1-14 2-13 3-12 4-11 5-15 6- 9 7- 8 10-18 16-17
1-18 2- 5 3-17 4-16 6-14 7-13 8-12 9-11 10-15
1- 6 2-10 3- 4 5- 7 8-17 9-16 11-14 12-13 15-18
1-11 2-15 3- 9 4- 8 5-12 6-18 7-10 13-17 14-16
1-16 2-18 3-14 4-13 5-17 6-11 7-15 8- 9 10-12
1- 3 2- 7 4- 5 6-16 8-14 9-13 10-17 11-18 12-15
1- 8 2-12 3- 6 4-10 5- 9 7-18 11-16 13-14 15-17
1-13 2-17 3-11 4-15 5-14 6- 8 7-12 9-10 16-18
1- 5 2- 4 3-16 6-13 7-17 8-11 9-15 10-14 12-18
1-10 2- 9 3-18 4- 7 5- 6 8-16 11-13 12-17 14-15
1-15 2-14 3- 8 4-12 5-11 6-10 7- 9 13-16 17-18
1- 2 3-13 4-17 5-16 6-15 7-14 8-18 9-12 10-11
1- 7 2- 6 3- 5 4-18 8-13 9-17 10-16 11-15 12-14
1-12 2-11 3-10 4- 9 5- 8 6- 7 13-18 14-17 15-16
1-17 2-16 3-15 4-14 5-13 6-12 7-11 8-10 9-18