>>46245927Suicune is attacked by Pokemon Hunters who poison the lake over and over to tire out and keep Suicune in one location.
>catching a SuicuneGou and Ash happened to come across it while checking out the area as Research Fellows and when they came across the hunters Suicune was poisoned and exhausted so he did the only thing he really knew to do to help it escape the net, he threw his Pokeball at it to at the very least pull it out of the Net. I don't think he even expected it to be caught but given its weakened state it stayed in. Like
>>46246073 Suicune eventually chose to stay with him but that's not mentioning that it first reacted violently when first released and froze its Pokeball. Hell Gou even tried to release it. Still don't worry he's not really going to get to use it as it stays at the Research Park to sleep but constantly moves around cleaning lakes around the world when Gou isnt there.