Witsel contributing at both ends
There are two key phases in Borussia Dortmund's midfield play. Within this system, Axel Witsel performs a key role in both those phases. Against Eintracht Frankfurt, when they're building out of the back, Witsel was able to tuck in with the centre-backs so that the full-backs could push up the pitch. Meanwhile, Delaney provided a passing option in the middle.
The second is in the final third with Witsel providing an option at the edge of the box or making a late run into the box as is required according to how the play develops. He did this as Delaney hangs slightly behind in anticipation of a counter-attack. Regardless, this involvement in attack was key in both of Dortmund's goals as he was involved in the build-up of the first one and provided the assist for the second.