Stripe head propagation has been investigated in ion‐implanted garnet films using high speed photography with 10 nsec laser pulse illumination. For a given in‐plane field applied along the stripe, the stripe head velocity increases linearly with drive until a peak drive is reached, beyond which the velocity drops. The peak velocity increases with in‐plane field magnitude and depends on which of the two directions parallel to the stripe that the in‐plane field is applied. Numerical calculations of the dynamic wall structure are made to predict the peak velocity as a function of in‐plane field magnitude and direction. The effect of the implanted layer is taken into account by using a surface pinning condition. Results show that velocity breakdown occurs when a horizontal Bloch line (HBL) is nucleated. The velocity asymmetry with respect to in‐plane field direction occurs because the HBL nucleates at opposite surfaces for the two in‐plane field directions. The implanted layer inhibits HBL nucleation by pinning the surface spins, thus producing a higher peak velocity.