Your board or playing field in Rush Royale is where your units are placed as you spawn them.
The Importance of Your Board
All your strength is in your board, so you should always try and focus on building it up.
If you play with support units, it is very important that you place your damage units adjacent (next) to the support units so they can work in synergy to deal a lot of damage.
You only have 15 tiles to place your units, so you must organize your board so that you can deal the highest possible damage you can to defeat bosses and clear waves of monsters.
Example
The board on the left is weak because the white Hex units are not adjacent to the yellow Inquisitor units. This means Inquisitors will not execute many enemies during the wave. Hex’s next to other Hexs’ provides no benefit whatsoever.
Contrarily, the board on the right is strong.
You have a high-rank Thunderer unit next to a mid-rank Hex unit to provide a lot of execution of the wave.
Then the rest of the board is mostly filled with Crystalmancer for high boss/miniboss damage.
