Catching and haltering a weanling for the first time is one of the highest-stakes early handling moments, because how it goes will either confirm for the foal that humans are safe and their requests are manageable, or that humans are predators that must be escaped. Getting it right the first time saves many hours of remedial work later.
The safest approach is to work in a small, safe enclosure — ideally a round pen or a small paddock with safe fencing and no obstacles — so that the foal cannot build up serious speed or distance between itself and the handler. A weanling that is chased around a large pasture in an unsuccessful catching attempt is learning exactly the wrong lesson: that running away works.
Approach the weanling calmly with relaxed body language, looking slightly away rather than making direct eye contact, which horses read as predatory intent. Allow the foal to move but follow at a walk, not a run, keeping pressure light and consistent. The moment the foal stops and faces you or shows curiosity, stop all forward movement and let the foal settle. Many trainers use a soft rope or arm extended toward the foal's shoulder rather than immediately reaching for the head — catching the neck or shoulder first and working the hand forward to place the halter is less threatening than reaching directly for the face.
Once the halter is on, do not immediately try to lead — simply hold the lead rope and allow the foal to stand and breathe before asking for any movement. The first haltering should end with the foal standing calmly rather than fighting, even if that means doing very little else in the first session.