Tracer's
Pulse Bomb ultimate ability allows her to throw a sticky bomb. This may seem daunting but isn't difficult. Build your ultimate by damaging bullet sponges like Roadhog or Reinhardt.
Once your ultimate is built, find a large unaware enemy and get up close to them and use the sticky bomb. Once stuck, a large
STUCK will appear on your screen. This is most easily done while on defense in my opinion. It is particularly easy to stick Reinhardt by blinking behind enemy lines and walking up behind them. Bastion can also be an easy target if you're able to be sneaky. You'll want to avoid small and fast enemies, as you are likely to miss.
If you'd like to learn more about tracer and this achievement, you can view this video: