Minecraft – Select teams using /tellraw command

The command to check if anyone on team red has killed an ocelot is

/testfor @a[score_leader_stat=1, team=red]

Note that there's an underscore between score and leader_stat, not an equal sign! Get the output of that command block and hook it into two other command blocks with

/tp @a[team=red] x y z
/tellraw @a {text:"Red Team has slain the Ocelot!", color:red}

In a 1.8 snapshot, you could also use

/title @a title {text:"Red Team has slain the Ocelot!", color:red}

to get a large text display. You will need a set of such command blocks for every team and every possible leader. Note that if red team's leader is an Ocelot as well, they will also win the game by killing their own leader.

To clarify Daniel's answer, you can assign a tag to a player when they click on a command in the chat using the following command in a tellraw command:

/scoreboard players tag @p add command_clicked

Then, in a repeating command block chain, you can execute the following 3 commands in order:

/say @a[tag=command_clicked]
/tp @a[tag=command_clicked] <destination>
/scoreboard players tag @a remove command_clicked