This page delves into slightly more advanced territory, and concerns itself with the timing of moves, a situation which usually arises later in the game.
From the other player's point of view, a "leak" is an opportunity.
Those squares become "reserved" since the original colour can't play there any more, but a different colour can.
By contrast, "contested" squares are still up for grabs: pieces belonging to either side can play on them.
The general rule to follow is "Contested BEFORE Reserved!", meaning you should grab what you can before the other guy does!
Here it is Red's turn, and we see two different areas.
One area, marked "A", is "secure" ... neither Yellow nor Green can play there - ever! - so Red can play there at his leisure.
But another area in the middle of the board, marked "B",
is still being contested - either Red OR Green can play there -
and whoever is first gets it.
Unfortunately, Red made the wrong choice, playing in the "safe" or "reserved" area (shown in pink below), rather than the "contested" area in the middle,
Green immediately took advantage, and captured that area with his O4 (shown in light green), gaining an extra 4 points in the process, and costing Red a similar amount.
Red *should* have played his own O4 there, blocking Green,
and saving the play of the V3 for later.
Blue has some places on the right for L4 and I3 moves which
are completely safe, and, at least for now, the top rows
belong to Yellow and Green together, as shown here.
The area in the middle (shown by dashed outline) is open to all three colors: Blue can play the U, Yellow can play the Square, or Green can play the I1 (blocking Blue).
On 5 consecutive moves, none of those plays were made!
Five Moves Later ...
Instead we had Blue L4 and I3, Yellow I5 and V3, and Green L4: all uncontested moves.
Finally, Blue had no choice but to play the U in the middle, winning that battle by default.
Yellow/Green still won the game, but gave up a bonus (of either
color) in the process.
