Blood Bowl

Very easy. Start a new campaign, choose your favorite race and start on Medium.

Play the 1st venue, win 4 games and the Achievement will unlock.

NOTE - these difficulty Achievements do NOT stack, so you will have to do this 3 times, on the different difficultys.

Start any competition and set difficulty to Normal mode.

I personally find the easiest teams to win with are Chaos and Dwarf, though Dwarf is a lot more "new player" friendly since many of their players start with the crucial "block" skill.

Key points to note:

1) Don't take un-necessary risks. Play your movement players first and any other players that will not require a dice roll to fulfil their goal
2) Next up play any 2+ dice blocks that are essential to your plan. Don't throw any blocks unless necessary before you've finished your movement phase.

Not really tricky, but sometimes the dice will work against you. Just keep at it.