Well:
"When the players got stronger they found that playing with "completely free" rules was in great favour of Black (the beginner of the game). It is also proved that there is a sure win for Black when playing with "completely free" rules."
(from http://www.renju.nu/r1rulhis.htm)
The rule "no-more-then-five for black" is one of "black" restrictions in renju.
(do skréše) Dež čekáš, až bodeš v něčem na taho, možeš bóchnót na "vechetat" o řádko "oževet" na dóležitym léstko, potem našteloj toďto hodnoto třeba na 30 sekond, abe se tě stav tvéch špilu oževoval rechléc. (Servant) (okázat šecke vechetávke)