Recently, massively-parallel many-core processors such as Intel Xeon Phi coprocessors have attracted researchers' attentions because various applications are significantly accelerated with those processors. In the field of high-performance computing, OpenMP is a standard programming model commonly used to parallelize a kernel loop for many-core processors. For hierarchical parallel processing, OpenMP version 4.0 or later allows programmers to group threads into multiple thread teams. In this paper, we first show the performance gain of using multiple thread teams even for one many-core processor. Then, we demonstrate that dynamic load balancing among those thread teams has a potential of significantly improving the performance of irregular workloads on a many-core processor. Although the current OpenMP specification does not offer such a dynamic load balancing mechanism, we discuss possible benefits of dynamic load balancing among thread teams through experiments using the Intel Xeon Phi coprocessor.