Blocking

Blocking means to prevent the opponent from connecting, and is one of the basic Hex skills.

Common blocking moves
Suppose Blue wants to prevent Red from connecting her stone to the edge:  The following three basic blocking moves are relatively common:

The adjacent block


The near block


The far block


How not to block
Not all blocking moves work in all circumstances. Adjacent blocks almost never work on their own, as the opponent can just walk around them. Consider what happens when Blue keeps playing adjacent blocks: 

Similarly, if Blue keeps playing near blocks, Red can just bridge to one side, resulting in a bridge ladder. 

Far blocks are also fraught with danger, as it is often a good response for Red to hang back and threaten to go in both directions. Consider this situation:  After Blue plays the far block, Red plays on the 4th row rather than the 3rd row, and can now connect to the edge via either of the cells marked "*" and a ziggurat.

Some common ways to block
Generally speaking, blocking is easier far from the edge than too close to it.

The best way to block very much depends on what is going on on the rest of the board. In many situations, it is a good idea to play a near block followed by an adjacent block, or an adjacent block followed by a near block.

Near block followed by adjacent block
 Blue plays a near block followed by an adjacent block, resulting in a bottleneck. Red does not immediately connect to the edge, but instead gets ladders in both directions.

This maneuver is often effective, but it also creates a weakness, namely the unprotected hex at "*". Depending on the rest of the board, Red may exploit this, for example by playing a ladder escape fork.

Adjacent block followed by near block
 Blue plays an adjacent block followed by a near block, resulting in what is sometimes called a one-sided bottleneck. Red can continue bridging to the left (if there is enough space), but only gets a 4th row ladder on the right.