HKRU community rugby manager Cameron Prouting said teams gained bonus points from scoring four or more tries, or by losing by less than seven points.
Should Foxton beat Shannon this weekend by more than seven points, and should Shannon fail to score four or more tries, the final semi-final berth would be decided by which team won the round robin matches.
As Toa and Shannon had one win apiece in their two encounters so far this year, it boiled down to bonus points accumulated.
As both sides had scored the same amount of bonus points for four tries or more (five) the next deciding factor was points differential. Just 10 points separated the points for and points against statistics for both teams.
That meant should Shannon lose this weekend their points differential would be lower than Toa's, meaning Toa would qualify for the semi-final anyway.
Should the points differential have been equal, it would boil down to the number of tries scored that season, where Toa held the advantage with 45 compared to Shannon's season haul of 39 tries.
Shannon has to come away from the Foxton game with a win or at least one bonus point from scoring four tries or losing by seven points or less, otherwise Toa goes through.
Shannon coach Justin Pape said his side isn't going to bog themselves down trying to figure out what they need in terms of bonus points from their last game - they just want to win their remaining match.
Pape said he had a full squad that was injury free and wasn't getting caught up in counting points as they wanted to beat Foxton. He said they could still qualify in third spot with a win this weekend.
"We're not going to focus on that too much. We'll be trying to win the game first and foremost," he said.
Foxton had the added advantage of celebrating their old-timers' day this weekend which would ensure a big crowd to Easton Park.
Meanwhile, Toa coach Richie Wineera said they would train this week as if they were going through to the semi-finals, and the team was planning on travelling north to Easton Park to watch the game.
"We can't control what happens now so we will train this week like we are in the semi-finals," he said.
Wineera was gracious in defeat from their match at the weekend and said Shannon deserved their success. He said if there was one team that they would want to go through ahead of them, it would be Shannon.
"Shannon deserved that win. They're a good side and if they do go through ahead of us then we are glad it's them. We have a lot of respect for Shannon," he said.
"We have been affected by a horror run of injuries I can tell you. But no excuses."
In other games at the weekend, Rahui cemented their spot in the top four with a solid 21-7 win over Paraparaumu at Paraparaumu Domain, while Waikanae shot to the top of the table with a comprehensive 38-5 win over College Old Boys at Waikanae Park.
SCOREBOARD
Ramsbottom Cup Premier Competition
At Paraparaumu Domain: Rahui: 21 (P. Connor-Phillips, M. Connor-Phillips, J. Winterburn tries; T. Manga 3 con) v Paraparaumu: 7 (O. Barr try; S. McBride con).
At Waikanae Park: Waikanae: 38 (G. Levave 2, B. Khanchaleun 2, T. Brown, E. Tamani tries; E. Reti 4 con) v Levin College Old Boys: 5 (J. Tupai-Ui try).
At Shannon Domain: Shannon: 32 (J. Tagavaitau 2, L. O'Connor 2, M. Halls tries; S. Pape con, H. Thomas con, pen) v Toa: 25.
Bill Muir Cup - Reserve Grade
At Playford Park: Foxton: 10 (R. Deadman, B Robinson tries) v Athletic: 7 (E. Pollock try; M. Easton con)
At Paraparaumu Domain: Paraparaumu: 69 (T. Davidson 2, P. Goldsmith 2, C. Voullaire 2, S. Mareikura-Martin, B. Windsor 2, M. Tambour, C. Mareikura-Martin 2 tries; P. Goldsmith 6 con, C. Mareikura-Martin con) v Rahui: 0.
