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) Održoj si přehledny Vzkaze skladovánim dóležitéch zpráv a co chvila pooživánim čudla Smáznót všecke zpráve v oddilo Zpráve, co přicházijó. (pauloaguia) (okázat šecke vechetávke)