I had to change few things but try this:

create table #groupings (

ID int,

EventName varchar(255),

Venue varchar(255),

EventDate datetime

)

insert into #groupings

select 1,'Football','Arena','2013-10-04 09:58:42.670'

UNion

select 2,'Football','Arena','2013-10-04 09:58:42.670'

union

select 3,'Football','Arena','2013-10-04 10:45:42.670'

union

select 4,'Football','Arena','2013-10-04 09:58:42.670'

union

select 1,'Soccer','Field','2013-10-04 09:58:42.670'

union

select 2,'Soccer','Field','2013-10-04 09:38:42.670'

union

select 3,'Soccer','Field','2013-10-04 09:58:42.670'

union

select 4,'Soccer','Field','2013-10-04 09:28:42.670'

select EventName, Venue, min(EventDate),

substring((select ',' + cast(ID as varchar)

from #groupings g1

where g1.EventName= g2.EventName

order by g1.EventName

for xml path ('')),2, 1000) [Students]

from #groupings g2

group by EventName, Venue