Join Two Tables and Get the values

Are these three tables have relationships? i.e., from Teams to team members to ride out events, do they have relationships in place?

Then try this. (Try first without ALL and try with ALL - one should work. )

TotalTeamMemberCount = 
Calculate( 
 DISTINCTCOUNT( IPME_TeamMembers[EmpId]), 
 FILTER ( ALL('RideOutEvents'), RideOutEvents [RideOutEventID ] = @EventId ),
                     -- Replace with your variable or value
 FILTER ( ALL('IPME_Teams'), IPME_Teams [SectionId] IN { 0, @SectionId)) 
                     -- Replace with your variable or value 
)