Net magnetic field at the centre of the circle O due to a current through a loop ABA as shown in figure $\left(\theta <180°\right)$. Take current flow in anti-clock wise direction in loop ABA.

The current through loop in anti location. Hence, magnetic field at the points within the loop in perpendicularly outward to the plane. The magnetic field lines from a closed path. A tangent to the field lines gives the directions of forces at same point. Thus, magnetic field at O is perpendicularly inward to the paper