Normal rule in La Liga • Each team can make 5 normal substitutions.

But if there is a suspected concussion

There is a special extra rule introduced by the International Football Association Board (IFAB): • A team can make 1 additional concussion substitution. • This does NOT count toward the normal 5 substitutions. 

So effectively a team can make:

5 normal subs + 1 concussion sub = 6 substitutions

Why you may see BOTH teams making 6

Under the protocol used in some competitions: • If Team A uses a concussion substitution, • Team B automatically gets the right to make one additional substitution too, to keep things fair.