The purpose of this study was to investigate the effects of alterations in the defensive strategies on physiological responses and time-motion characteristics during 3 x 4 min small-sided games (SSGs) in young soccer players. Eighteen young soccer players (age 19.6 +/- 0.5 years, body height 178.3 +/- 4.6 cm, body mass 71.9 +/- 7.5 kg and VO2max 49.51 +/- 2.44 ml.kg(-1).min(-1)) voluntarily participated in SSGs with different defensive strategies (FP: free play, MM: man-marking, DMP: double-man pressure). Heart rate (HR) and total distance covered in different speed zones were monitored during all SSGs, whereas the session-rating of perceived exertion (session-RPE, CR-10) and venous blood lactate (La-) were determined at the end of the last bout of each SSG. The results demonstrated that DMP produced significantly higher La- (F=23.82, p<.05, eta(2)=0.58), HR (F=10.10; p<.05; eta(2)=0.37), % HRmax (F=81.11; p<.05; eta(2)=0.82), and session-RPE (F=215.63, p<.05, eta(2)=0.92) responses compared to FP and MM. Furthermore, significant differences were found between MM and FP condition. In addition, during the DMP, players covered greater distances in the high-intensity running zone (>18 km.h(-1)) (F=13.67; p<.05; eta(2)=0.44) compared to MM and FP. The findings of this study revealed that the alterations in the defensive strategies brought about different physiological responses and time-motion characteristics during the course of SSGs. Therefore, the recommendation for coaches is to choose DMP or MM defensive strategies if they target higher physiological responses and time-motion characteristics during the SSGs.