why does sb keep coldcalling

[Get_better_Baris]

Poker Stars, $2/$4 NL Hold'em Cash Game, 6 Players
LegoPoker Hand History Converter

MP: $544
CO: $516.50
BTN: $430
SB: $382
Hero (BB): $400
UTG: $377.10

Pre-Flop: 4[img]/images/graemlins/diamond.gif[/img] 6[img]/images/graemlins/diamond.gif[/img] dealt to Hero (BB)
UTG calls $4, 3 folds, SB calls $2, Hero checks

Flop: ($12) 4[img]/images/graemlins/heart.gif[/img] T[img]/images/graemlins/diamond.gif[/img] 6[img]/images/graemlins/club.gif[/img] (3 Players)
SB checks, <font color="red">Hero bets $8</font>, <font color="red">UTG raises to $20</font>, SB calls $20, <font color="red">Hero raises to $100</font>, <font color="red">UTG raises to $180</font>, SB calls $160, Hero ?
i put utg on a big pair trying to lrr but wtf is up with sb. first hand at table no reads. i tryed to search for sb but he was hiding from search