Othello Midgame Strategy: Frontier Discs, Internal Moves, and Mobility

In Othello, winning the corners (see the X-squares and C-squares article) and reading the endgame (see that article) are vital — but how you play the midgame in between also decides games. The keys are internal moves (nakawari) and open-degree: both are about keeping your own moves available while shrinking your opponent's.

Why frontier discs are weak

A disc that touches an empty square is a frontier disc. Frontier discs can be flipped, and they hand your opponent new squares to play on (mobility). Internal discs — those surrounded by other discs — are not immediately flippable and do not add to your opponent's moves. So the midgame rule of thumb is: don't pile up frontier discs (corner-anchored stable discs aside). Counterintuitively, the player showing fewer discs on the board is often the one in control.

Nakawari — play inside to avoid new frontier discs

Nakawari means playing into an internal empty point surrounded by your own discs, so that the move flips only discs that are already enclosed. Because it creates almost no new frontier discs, it keeps your shape intact and gives your opponent few new squares to play. It flips only a handful of discs and looks quiet, but it is a strong mobility-preserving move.

Open-degree — count the empties next to the discs you flip

To compare candidate moves, count the empty squares adjacent to the discs that the move would flip — this is the move's open-degree. The lower the open-degree, the fewer new frontier discs you create, and generally the better the move (this is open-degree theory). A nakawari is the lowest-open-degree case. When you are unsure, choose the move that opens up the fewest empties.

Strangling mobility — the midgame plan

Keep playing low-open-degree and nakawari moves, and your own moves stay available while your opponent's shrink — until they are forced to play a bad square, such as one next to a corner (an X-square or C-square). This is how you strangle the opponent's mobility in the midgame. Flipping fewer discs by keeping your open-degree low beats greedily flipping many — that is the heart of the Othello paradox that 'flipping the most discs loses'.

How to practice

Use TsumeDojo's tsume Othello (forced-win endgame problems) to sharpen your reading to the last square, and in your own games during the midgame, ask of each move: 'what is its open-degree — can I play a nakawari instead?' Keeping your open-degree low to preserve mobility lets you build an advantage well before the endgame arrives.